チュートリアル: AWS SDK を使用したデータ検証 - Amazon Quantum Ledger Database (Amazon QLDB)
前提条件ステップ 1: ダイジェストをリクエストするステップ 2: ドキュメントリビジョンをクエリするステップ 3: リビジョンの証明をリクエストするステップ 4: リビジョンのダイジェストを再計算するステップ 5: ジャーナルブロックの証明をリクエストするステップ 6: ブロックのダイジェストを再計算する完全なコード例を実行する

翻訳は機械翻訳により提供されています。提供された翻訳内容と英語版の間で齟齬、不一致または矛盾がある場合、英語版が優先します。

チュートリアル: AWS SDK を使用したデータ検証

このチュートリアルでは、 AWS SDK を介して QLDB API を使用して、Amazon QLDB 台帳のドキュメントリビジョンハッシュとジャーナルブロックハッシュを検証します。QLDB ドライバーを使用して、ドキュメントリビジョンのクエリも実行します。

車両識別番号 (VIN、Vehicle Identification Number) が KM8SRDHF6EU074761 である車両のデータを含むドキュメントリビジョンがあるとします。ドキュメントリビジョンはテーブル VehicleRegistration にあり、このテーブルは台帳 vehicle-registration にあります。この車両のドキュメントリビジョンとこのリビジョンを含むジャーナルブロックの両方の整合性を検証するとします。

注記

現実的なユースケースにおける暗号化検証の価値について説明する詳細な AWS ブログ記事については、「Amazon QLDB による実際の暗号化検証」を参照してください。

前提条件

作業を始める前に、次の操作を実行してください。

  1. 「Amazon QLDB ドライバーの開始方法」で述べた各前提条件を満たすことにより、目的の言語の QLDB ドライバーを設定します。これには、 へのサインアップ AWS、開発用のプログラムによるアクセスの付与、開発環境の設定が含まれます。

  2. 「Amazon QLDB コンソールの使用開始方法」のステップ 1～2 を実行して、台帳 vehicle-registration を作成し、事前定義済みのサンプルデータを使用してロードします。

この後、以下のステップを確認して検証の仕組みを学習し、完全なコード例を最初から最後まで実行します。

ステップ 1: ダイジェストをリクエストする

データを検証するには、まず台帳 vehicle-registration に後で使用するダイジェストをリクエストする必要があります。

Java
// Get a digest
GetDigestRequest digestRequest = new GetDigestRequest().withName(ledgerName);
GetDigestResult digestResult = client.getDigest(digestRequest);

java.nio.ByteBuffer digest = digestResult.getDigest();

// expectedDigest is the buffer we will use later to compare against our calculated digest
byte[] expectedDigest = new byte[digest.remaining()];
digest.get(expectedDigest);
.NET
// Get a digest
GetDigestRequest getDigestRequest = new GetDigestRequest
{
    Name = ledgerName
};
GetDigestResponse getDigestResponse = client.GetDigestAsync(getDigestRequest).Result;

// expectedDigest is the buffer we will use later to compare against our calculated digest
MemoryStream digest = getDigestResponse.Digest;
byte[] expectedDigest = digest.ToArray();
Go
// Get a digest
currentLedgerName := ledgerName
input := qldb.GetDigestInput{Name: &currentLedgerName}
digestOutput, err := client.GetDigest(&input)
if err != nil {
    panic(err)
}

// expectedDigest is the buffer we will later use to compare against our calculated digest
expectedDigest := digestOutput.Digest
Node.js
// Get a digest
const getDigestRequest: GetDigestRequest = {
    Name: ledgerName
};
const getDigestResponse: GetDigestResponse = await qldbClient.getDigest(getDigestRequest).promise();

// expectedDigest is the buffer we will later use to compare against our calculated digest
const expectedDigest: Uint8Array = <Uint8Array>getDigestResponse.Digest;
Python
# Get a digest
get_digest_response = qldb_client.get_digest(Name=ledger_name)

# expected_digest is the buffer we will later use to compare against our calculated digest
expected_digest = get_digest_response.get('Digest')
digest_tip_address = get_digest_response.get('DigestTipAddress')

ステップ 2: ドキュメントリビジョンをクエリする

QLDB ドライバーを使用して、VIN KM8SRDHF6EU074761 に関連付けられているブロックアドレス、ハッシュ、ドキュメント ID をクエリします。

Java
// Retrieve info for the given vin's document revisions
Result result = driver.execute(txn -> {
    final String query = String.format("SELECT blockAddress, hash, metadata.id FROM _ql_committed_%s WHERE data.VIN = '%s'", tableName, vin);
    return txn.execute(query);
});
.NET
// Retrieve info for the given vin's document revisions
var result = driver.Execute(txn => {
    string query = $"SELECT blockAddress, hash, metadata.id FROM _ql_committed_{tableName} WHERE data.VIN = '{vin}'";
    return txn.Execute(query);
});
Go
// Retrieve info for the given vin's document revisions
result, err := driver.Execute(context.Background(), func(txn qldbdriver.Transaction) (interface{}, error) {
    statement := fmt.Sprintf(
            "SELECT blockAddress, hash, metadata.id FROM _ql_committed_%s WHERE data.VIN = '%s'",
            tableName,
            vin)
    result, err := txn.Execute(statement)
    if err != nil {
        return nil, err
    }

    results := make([]map[string]interface{}, 0)

    // Convert the result set into a map
    for result.Next(txn) {
        var doc map[string]interface{}
        err := ion.Unmarshal(result.GetCurrentData(), &doc)
        if err != nil {
            return nil, err
        }
        results = append(results, doc)
    }
    return results, nil
})
if err != nil {
    panic(err)
}
resultSlice := result.([]map[string]interface{})
Node.js
const result: dom.Value[] = await driver.executeLambda(async (txn: TransactionExecutor): Promise<dom.Value[]> => {
    const query: string = `SELECT blockAddress, hash, metadata.id FROM _ql_committed_${tableName} WHERE data.VIN = '${vin}'`;
    const queryResult: Result = await txn.execute(query);
    return queryResult.getResultList();
});
Python
def query_doc_revision(txn):
    query = "SELECT blockAddress, hash, metadata.id FROM _ql_committed_{} WHERE data.VIN = '{}'".format(table_name, vin)
    return txn.execute_statement(query)

# Retrieve info for the given vin's document revisions
result = qldb_driver.execute_lambda(query_doc_revision)

ステップ 3: リビジョンの証明をリクエストする

クエリ結果を反復処理し、各ブロックアドレス、ドキュメント ID および台帳名を使用して、GetRevision リクエストを実行します。リビジョンの証明を取得するには、以前に保存したダイジェストのティップアドレスも指定する必要があります。以下の API オペレーションは、ドキュメントリビジョンとリビジョンの証明を含むオブジェクトを返します。

リビジョンの構造と内容の詳細については、「ドキュメントのメタデータのクエリの実行」を参照してください。

Java
for (IonValue ionValue : result) {
    IonStruct ionStruct = (IonStruct)ionValue;

    // Get the requested fields
    IonValue blockAddress = ionStruct.get("blockAddress");
    IonBlob hash = (IonBlob)ionStruct.get("hash");
    String metadataId = ((IonString)ionStruct.get("id")).stringValue();

    System.out.printf("Verifying document revision for id '%s'%n", metadataId);

    String blockAddressText = blockAddress.toString();

    // Submit a request for the revision
    GetRevisionRequest revisionRequest = new GetRevisionRequest()
            .withName(ledgerName)
            .withBlockAddress(new ValueHolder().withIonText(blockAddressText))
            .withDocumentId(metadataId)
            .withDigestTipAddress(digestResult.getDigestTipAddress());

    // Get a result back
    GetRevisionResult revisionResult = client.getRevision(revisionRequest);

    ...
}
.NET
foreach (IIonValue ionValue in result)
{
    IIonStruct ionStruct = ionValue;

    // Get the requested fields
    IIonValue blockAddress = ionStruct.GetField("blockAddress");
    IIonBlob hash = ionStruct.GetField("hash");
    String metadataId = ionStruct.GetField("id").StringValue;

    Console.WriteLine($"Verifying document revision for id '{metadataId}'");

    // Use an Ion Reader to convert block address to text
    IIonReader reader = IonReaderBuilder.Build(blockAddress);
    StringWriter sw = new StringWriter();
    IIonWriter textWriter = IonTextWriterBuilder.Build(sw);
    textWriter.WriteValues(reader);
    string blockAddressText = sw.ToString();

    // Submit a request for the revision
    GetRevisionRequest revisionRequest = new GetRevisionRequest
    {
        Name = ledgerName,
        BlockAddress = new ValueHolder
        {
            IonText = blockAddressText
        },
        DocumentId = metadataId,
        DigestTipAddress = getDigestResponse.DigestTipAddress
    };
    
    // Get a response back
    GetRevisionResponse revisionResponse = client.GetRevisionAsync(revisionRequest).Result;

    ...
}
Go
for _, value := range resultSlice {
    // Get the requested fields
    ionBlockAddress, err := ion.MarshalText(value["blockAddress"])
    if err != nil {
        panic(err)
    }
    blockAddress := string(ionBlockAddress)
    metadataId := value["id"].(string)
    documentHash := value["hash"].([]byte)

    fmt.Printf("Verifying document revision for id '%s'\n", metadataId)

    // Submit a request for the revision
    revisionInput := qldb.GetRevisionInput{
        BlockAddress:     &qldb.ValueHolder{IonText: &blockAddress},
        DigestTipAddress: digestOutput.DigestTipAddress,
        DocumentId:       &metadataId,
        Name:             &currentLedgerName,
    }

    // Get a result back
    revisionOutput, err := client.GetRevision(&revisionInput)
    if err != nil {
        panic(err)
    }

    ...
}
Node.js
for (let value of result) {
    // Get the requested fields
    const blockAddress: dom.Value = value.get("blockAddress");
    const hash: dom.Value = value.get("hash");
    const metadataId: string = value.get("id").stringValue();

    console.log(`Verifying document revision for id '${metadataId}'`);

    // Submit a request for the revision
    const revisionRequest: GetRevisionRequest = {
        Name: ledgerName,
        BlockAddress: {
            IonText: dumpText(blockAddress)
        },
        DocumentId: metadataId,
        DigestTipAddress: getDigestResponse.DigestTipAddress
    };

    // Get a response back
    const revisionResponse: GetRevisionResponse = await qldbClient.getRevision(revisionRequest).promise();

    ...
}
Python
for value in result:
    # Get the requested fields
    block_address = value['blockAddress']
    document_hash = value['hash']
    metadata_id = value['id']

    print("Verifying document revision for id '{}'".format(metadata_id))

    # Submit a request for the revision and get a result back
    proof_response = qldb_client.get_revision(Name=ledger_name,
                                              BlockAddress=block_address_to_dictionary(block_address),
                                              DocumentId=metadata_id,
                                              DigestTipAddress=digest_tip_address)

次に、リクエストしたリビジョンの証明を取得します。

QLDB API は、ノードハッシュの順序付きリストの文字列表現として証明を返します。この文字列をノードハッシュのバイナリ表現のリストに変換するには、Amazon Ion ライブラリの Ion リーダーを使用します。Ion ライブラリの使用方法については、「Amazon Ion Cookbook」(Amazon Ion クックブック) を参照してください。

Java

次の例では、IonReader を使用してバイナリ変換を実行します。

String proofText = revisionResult.getProof().getIonText();

// Take the proof and convert it to a list of byte arrays
List<byte[]> internalHashes = new ArrayList<>();
IonReader reader = SYSTEM.newReader(proofText);
reader.next();
reader.stepIn();
while (reader.next() != null) {
    internalHashes.add(reader.newBytes());
}
.NET

次の例では、IonLoader を使用して証明を Ion データグラムにロードします。

string proofText = revisionResponse.Proof.IonText;
IIonDatagram proofValue = IonLoader.Default.Load(proofText);
Go

次の例では、Ion リーダーを使用して証明をバイナリに変換し、証明のノードハッシュのリストを反復処理します。

proofText := revisionOutput.Proof.IonText

// Use ion.Reader to iterate over the proof's node hashes
reader := ion.NewReaderString(*proofText)
// Enter the struct containing node hashes
reader.Next()
if err := reader.StepIn(); err != nil {
    panic(err)
}
Node.js

次の例では、load 関数を使用してバイナリ変換を実行します。

let proofValue: dom.Value = load(revisionResponse.Proof.IonText);
Python

次の例では、loads 関数を使用してバイナリ変換を実行します。

proof_text = proof_response.get('Proof').get('IonText')
proof_hashes = loads(proof_text)

ステップ 4: リビジョンのダイジェストを再計算する

証明のハッシュリストを使用して、ダイジェストを再計算します。これは、リビジョンハッシュから始めます。過去に保存されたダイジェストがわかっており、QLDB の外部で信頼されている限り、ドキュメントリビジョンの整合性は、再計算したダイジェストハッシュが保存されているダイジェストハッシュと一致した場合に証明されます。

Java
// Calculate digest
byte[] calculatedDigest = internalHashes.stream().reduce(hash.getBytes(), BlockHashVerification::dot);

boolean verified = Arrays.equals(expectedDigest, calculatedDigest);

if (verified) {
    System.out.printf("Successfully verified document revision for id '%s'!%n", metadataId);
} else {
    System.out.printf("Document revision for id '%s' verification failed!%n", metadataId);
    return;
}
.NET
byte[] documentHash = hash.Bytes().ToArray();
foreach (IIonValue proofHash in proofValue.GetElementAt(0))
{
    // Calculate the digest
    documentHash = Dot(documentHash, proofHash.Bytes().ToArray());
}

bool verified = expectedDigest.SequenceEqual(documentHash);

if (verified)
{
    Console.WriteLine($"Successfully verified document revision for id '{metadataId}'!");
}
else
{
    Console.WriteLine($"Document revision for id '{metadataId}' verification failed!");
    return;
}
Go
// Going through nodes and calculate digest
for reader.Next() {
    val, _ := reader.ByteValue()
    documentHash, err = dot(documentHash, val)
}

// Compare documentHash with the expected digest
verified := reflect.DeepEqual(documentHash, expectedDigest)

if verified {
    fmt.Printf("Successfully verified document revision for id '%s'!\n", metadataId)
} else {
    fmt.Printf("Document revision for id '%s' verification failed!\n", metadataId)
    return
}
Node.js
let documentHash: Uint8Array = hash.uInt8ArrayValue();
proofValue.elements().forEach((proofHash: dom.Value) => {
    // Calculate the digest
    documentHash = dot(documentHash, proofHash.uInt8ArrayValue());
});

let verified: boolean = isEqual(expectedDigest, documentHash);

if (verified) {
    console.log(`Successfully verified document revision for id '${metadataId}'!`);
} else {
    console.log(`Document revision for id '${metadataId}' verification failed!`);
    return;
}
Python
# Calculate digest
calculated_digest = reduce(dot, proof_hashes, document_hash)

verified = calculated_digest == expected_digest
if verified:
    print("Successfully verified document revision for id '{}'!".format(metadata_id))
else:
    print("Document revision for id '{}' verification failed!".format(metadata_id))

ステップ 5: ジャーナルブロックの証明をリクエストする

次に、ドキュメントリビジョンを含むジャーナルブロックを検証します。

ステップ 1 で保存したダイジェストのブロックアドレスとティップアドレスを使用して、GetBlock リクエストを実行します。ステップ 2 の GetRevision リクエストと同様に、保存されたダイジェストのティップアドレスを再度指定してブロックの証明を取得する必要があります。以下の API オペレーションは、ブロックとブロックの証明を含むオブジェクトを返します。

ジャーナルブロックの構造と内容の詳細については、「Amazon QLDB のジャーナルコンテンツ」を参照してください。

Java
// Submit a request for the block
GetBlockRequest getBlockRequest = new GetBlockRequest()
        .withName(ledgerName)
        .withBlockAddress(new ValueHolder().withIonText(blockAddressText))
        .withDigestTipAddress(digestResult.getDigestTipAddress());

// Get a result back
GetBlockResult getBlockResult = client.getBlock(getBlockRequest);
.NET
// Submit a request for the block
GetBlockRequest getBlockRequest = new GetBlockRequest
{
    Name = ledgerName,
    BlockAddress = new ValueHolder
    {
        IonText = blockAddressText
    },
    DigestTipAddress = getDigestResponse.DigestTipAddress
};

// Get a response back
GetBlockResponse getBlockResponse = client.GetBlockAsync(getBlockRequest).Result;
Go
// Submit a request for the block
blockInput := qldb.GetBlockInput{
    Name:             &currentLedgerName,
    BlockAddress:     &qldb.ValueHolder{IonText: &blockAddress},
    DigestTipAddress: digestOutput.DigestTipAddress,
}

// Get a result back
blockOutput, err := client.GetBlock(&blockInput)
if err != nil {
    panic(err)
}
Node.js
// Submit a request for the block
const getBlockRequest: GetBlockRequest = {
    Name: ledgerName,
    BlockAddress: {
        IonText: dumpText(blockAddress)
    },
    DigestTipAddress: getDigestResponse.DigestTipAddress
};

// Get a response back
const getBlockResponse: GetBlockResponse = await qldbClient.getBlock(getBlockRequest).promise();
Python
def block_address_to_dictionary(ion_dict):
"""
Convert a block address from IonPyDict into a dictionary.
Shape of the dictionary must be: {'IonText': "{strandId: <"strandId">, sequenceNo: <sequenceNo>}"}

:type ion_dict: :py:class:`amazon.ion.simple_types.IonPyDict`/str
:param ion_dict: The block address value to convert.

:rtype: dict
:return: The converted dict.
"""
block_address = {'IonText': {}}
if not isinstance(ion_dict, str):
    py_dict = '{{strandId: "{}", sequenceNo:{}}}'.format(ion_dict['strandId'], ion_dict['sequenceNo'])
    ion_dict = py_dict
block_address['IonText'] = ion_dict
return block_address

# Submit a request for the block and get a result back
block_response = qldb_client.get_block(Name=ledger_name, BlockAddress=block_address_to_dictionary(block_address),
                                       DigestTipAddress=digest_tip_address)

次に、結果からブロックハッシュと証明を取得します。

Java

次の例では、IonLoader を使用してブロックオブジェクトを IonDatagram コンテナにロードします。

String blockText = getBlockResult.getBlock().getIonText();

IonDatagram datagram = SYSTEM.getLoader().load(blockText);
ionStruct = (IonStruct)datagram.get(0);

final byte[] blockHash = ((IonBlob)ionStruct.get("blockHash")).getBytes();

また、IonLoader を使用して証明を IonDatagram にロードします。

proofText = getBlockResult.getProof().getIonText();

// Take the proof and create a list of hash binary data
datagram = SYSTEM.getLoader().load(proofText);
ListIterator<IonValue> listIter = ((IonList)datagram.iterator().next()).listIterator();

internalHashes.clear();
while (listIter.hasNext()) {
    internalHashes.add(((IonBlob)listIter.next()).getBytes());
}
.NET

次の例では、IonLoader を使用してブロックと証明をそれぞれ Ion データグラムにロードします。

string blockText = getBlockResponse.Block.IonText;
IIonDatagram blockValue = IonLoader.Default.Load(blockText);

// blockValue is a IonDatagram, and the first value is an IonStruct containing the blockHash
byte[] blockHash = blockValue.GetElementAt(0).GetField("blockHash").Bytes().ToArray();

proofText = getBlockResponse.Proof.IonText;
proofValue = IonLoader.Default.Load(proofText);
Go

次の例では、Ion リーダーを使用して証明をバイナリに変換し、証明のノードハッシュのリストを反復処理します。

proofText = blockOutput.Proof.IonText

block := new(map[string]interface{})
err = ion.UnmarshalString(*blockOutput.Block.IonText, block)
if err != nil {
    panic(err)
}

blockHash := (*block)["blockHash"].([]byte)

// Use ion.Reader to iterate over the proof's node hashes
reader = ion.NewReaderString(*proofText)
// Enter the struct containing node hashes
reader.Next()
if err := reader.StepIn(); err != nil {
    panic(err)
}
Node.js

次の例では、load 関数を使用してブロックと証明をバイナリに変換します。

const blockValue: dom.Value = load(getBlockResponse.Block.IonText)
let blockHash: Uint8Array = blockValue.get("blockHash").uInt8ArrayValue();

proofValue = load(getBlockResponse.Proof.IonText);
Python

次の例では、loads 関数を使用してブロックと証明をバイナリに変換します。

block_text = block_response.get('Block').get('IonText')
block = loads(block_text)

block_hash = block.get('blockHash')

proof_text = block_response.get('Proof').get('IonText')
proof_hashes = loads(proof_text)

ステップ 6: ブロックのダイジェストを再計算する

証明のハッシュリストを使用して、ダイジェストを再計算します。これは、ブロックハッシュから始めます。過去に保存されたダイジェストがわかっており、QLDB の外部で信頼されている限り、ブロックの整合性は、再計算したダイジェストハッシュが保存されているダイジェストハッシュと一致した場合に証明されます。

Java
// Calculate digest
calculatedDigest = internalHashes.stream().reduce(blockHash, BlockHashVerification::dot);

verified = Arrays.equals(expectedDigest, calculatedDigest);

if (verified) {
    System.out.printf("Block address '%s' successfully verified!%n", blockAddressText);
} else {
    System.out.printf("Block address '%s' verification failed!%n", blockAddressText);
}
.NET
foreach (IIonValue proofHash in proofValue.GetElementAt(0))
{
    // Calculate the digest
    blockHash = Dot(blockHash, proofHash.Bytes().ToArray());
}

verified = expectedDigest.SequenceEqual(blockHash);

if (verified)
{
    Console.WriteLine($"Block address '{blockAddressText}' successfully verified!");
}
else
{
    Console.WriteLine($"Block address '{blockAddressText}' verification failed!");
}
Go
// Going through nodes and calculate digest
for reader.Next() {
    val, err := reader.ByteValue()
    if err != nil {
        panic(err)
    }
    blockHash, err = dot(blockHash, val)
}

// Compare blockHash with the expected digest
verified = reflect.DeepEqual(blockHash, expectedDigest)

if verified {
    fmt.Printf("Block address '%s' successfully verified!\n", blockAddress)
} else {
    fmt.Printf("Block address '%s' verification failed!\n", blockAddress)
    return
}
Node.js
proofValue.elements().forEach((proofHash: dom.Value) => {
    // Calculate the digest
    blockHash = dot(blockHash, proofHash.uInt8ArrayValue());
});

verified = isEqual(expectedDigest, blockHash);

if (verified) {
    console.log(`Block address '${dumpText(blockAddress)}' successfully verified!`);
} else {
    console.log(`Block address '${dumpText(blockAddress)}' verification failed!`);
}
Python
# Calculate digest
calculated_digest = reduce(dot, proof_hashes, block_hash)

verified = calculated_digest == expected_digest
if verified:
    print("Block address '{}' successfully verified!".format(dumps(block_address,
                                                                   binary=False,
                                                                   omit_version_marker=True)))
else:
    print("Block address '{}' verification failed!".format(block_address))

上のコード例では、ダイジェストの再計算の際に以下の dot 関数を使用しています。この関数に 2 つのハッシュを入力すると、それらを並べ替え、連結して、連結された配列のハッシュを返します。

Java
/**
 * Takes two hashes, sorts them, concatenates them, and then returns the
 * hash of the concatenated array.
 *
 * @param h1
 *              Byte array containing one of the hashes to compare.
 * @param h2
 *              Byte array containing one of the hashes to compare.
 * @return the concatenated array of hashes.
 */
public static byte[] dot(final byte[] h1, final byte[] h2) {
    if (h1.length != HASH_LENGTH || h2.length != HASH_LENGTH) {
        throw new IllegalArgumentException("Invalid hash.");
    }

    int byteEqual = 0;
    for (int i = h1.length - 1; i >= 0; i--) {
        byteEqual = Byte.compare(h1[i], h2[i]);
        if (byteEqual != 0) {
            break;
        }
    }

    byte[] concatenated = new byte[h1.length + h2.length];
    if (byteEqual < 0) {
        System.arraycopy(h1, 0, concatenated, 0, h1.length);
        System.arraycopy(h2, 0, concatenated, h1.length, h2.length);
    } else {
        System.arraycopy(h2, 0, concatenated, 0, h2.length);
        System.arraycopy(h1, 0, concatenated, h2.length, h1.length);
    }

    MessageDigest messageDigest;
    try {
        messageDigest = MessageDigest.getInstance("SHA-256");
    } catch (NoSuchAlgorithmException e) {
        throw new IllegalStateException("SHA-256 message digest is unavailable", e);
    }

    messageDigest.update(concatenated);
    return messageDigest.digest();
}
.NET
/// <summary>
/// Takes two hashes, sorts them, concatenates them, and then returns the
/// hash of the concatenated array.
/// </summary>
/// <param name="h1">Byte array containing one of the hashes to compare.</param>
/// <param name="h2">Byte array containing one of the hashes to compare.</param>
/// <returns>The concatenated array of hashes.</returns>
private static byte[] Dot(byte[] h1, byte[] h2)
{
    if (h1.Length == 0)
    {
        return h2;
    }

    if (h2.Length == 0)
    {
        return h1;
    }

    HashAlgorithm hashAlgorithm = HashAlgorithm.Create("SHA256");
    HashComparer comparer = new HashComparer();
    if (comparer.Compare(h1, h2) < 0)
    {
        return hashAlgorithm.ComputeHash(h1.Concat(h2).ToArray());
    }
    else
    {
        return hashAlgorithm.ComputeHash(h2.Concat(h1).ToArray());
    }
}

private class HashComparer : IComparer<byte[]>
{
    private static readonly int HASH_LENGTH = 32;

    public int Compare(byte[] h1, byte[] h2)
    {
        if (h1.Length != HASH_LENGTH || h2.Length != HASH_LENGTH)
        {
            throw new ArgumentException("Invalid hash");
        }

        for (var i = h1.Length - 1; i >= 0; i--)
        {
            var byteEqual = (sbyte)h1[i] - (sbyte)h2[i];
            if (byteEqual != 0)
            {
                return byteEqual;
            }
        }

        return 0;
    }
}
Go
// Takes two hashes, sorts them, concatenates them, and then returns the hash of the concatenated array.
func dot(h1, h2 []byte) ([]byte, error) {
    compare, err := hashComparator(h1, h2)
    if err != nil {
        return nil, err
    }

    var concatenated []byte
    if compare < 0 {
        concatenated = append(h1, h2...)
    } else {
        concatenated = append(h2, h1...)
    }

    newHash := sha256.Sum256(concatenated)
    return newHash[:], nil
}

func hashComparator(h1 []byte, h2 []byte) (int16, error) {
    if len(h1) != hashLength || len(h2) != hashLength {
        return 0, errors.New("invalid hash")
    }
    for i := range h1 {
        // Reverse index for little endianness
        index := hashLength - 1 - i

        // Handle byte being unsigned and overflow
        h1Int := int16(h1[index])
        h2Int := int16(h2[index])
        if h1Int > 127 {
            h1Int = 0 - (256 - h1Int)
        }
        if h2Int > 127 {
            h2Int = 0 - (256 - h2Int)
        }

        difference := h1Int - h2Int
        if difference != 0 {
            return difference, nil
        }
    }
    return 0, nil
}
Node.js
/**
 * Takes two hashes, sorts them, concatenates them, and calculates a digest based on the concatenated hash.
 * @param h1 Byte array containing one of the hashes to compare.
 * @param h2 Byte array containing one of the hashes to compare.
 * @returns The digest calculated from the concatenated hash values.
 */
function dot(h1: Uint8Array, h2: Uint8Array): Uint8Array {
    if (h1.length === 0) {
        return h2;
    }
    if (h2.length === 0) {
        return h1;
    }

    const newHashLib = createHash("sha256");

    let concatenated: Uint8Array;
    if (hashComparator(h1, h2) < 0) {
        concatenated = concatenate(h1, h2);
    } else {
        concatenated = concatenate(h2, h1);
    }
    newHashLib.update(concatenated);
    return newHashLib.digest();
}

/**
 * Compares two hashes by their **signed** byte values in little-endian order.
 * @param hash1 The hash value to compare.
 * @param hash2 The hash value to compare.
 * @returns Zero if the hash values are equal, otherwise return the difference of the first pair of non-matching
 *          bytes.
 * @throws RangeError When the hash is not the correct hash size.
 */
function hashComparator(hash1: Uint8Array, hash2: Uint8Array): number {
    if (hash1.length !== HASH_SIZE || hash2.length !== HASH_SIZE) {
        throw new RangeError("Invalid hash.");
    }
    for (let i = hash1.length-1; i >= 0; i--) {
        const difference: number = (hash1[i]<<24 >>24) - (hash2[i]<<24 >>24);
        if (difference !== 0) {
            return difference;
        }
    }
    return 0;
}

/**
 * Helper method that concatenates two Uint8Array.
 * @param arrays List of arrays to concatenate, in the order provided.
 * @returns The concatenated array.
 */
function concatenate(...arrays: Uint8Array[]): Uint8Array {
    let totalLength = 0;
    for (const arr of arrays) {
        totalLength += arr.length;
    }
    const result = new Uint8Array(totalLength);
    let offset = 0;
    for (const arr of arrays) {
        result.set(arr, offset);
        offset += arr.length;
    }
    return result;
}

/**
 * Helper method that checks for equality between two Uint8Array.
 * @param expected Byte array containing one of the hashes to compare.
 * @param actual Byte array containing one of the hashes to compare.
 * @returns Boolean indicating equality between the two Uint8Array.
 */
function isEqual(expected: Uint8Array, actual: Uint8Array): boolean {
    if (expected === actual) return true;
    if (expected == null || actual == null) return false;
    if (expected.length !== actual.length) return false;

    for (let i = 0; i < expected.length; i++) {
        if (expected[i] !== actual[i]) {
            return false;
        }
    }
    return true;
}
Python
def dot(hash1, hash2):
    """
    Takes two hashes, sorts them, concatenates them, and then returns the
    hash of the concatenated array.

    :type hash1: bytes
    :param hash1: The hash value to compare.

    :type hash2: bytes
    :param hash2: The hash value to compare.

    :rtype: bytes
    :return: The new hash value generated from concatenated hash values.
    """
    if len(hash1) != hash_length or len(hash2) != hash_length:
        raise ValueError('Illegal hash.')

    hash_array1 = array('b', hash1)
    hash_array2 = array('b', hash2)

    difference = 0
    for i in range(len(hash_array1) - 1, -1, -1):
        difference = hash_array1[i] - hash_array2[i]
        if difference != 0:
            break

    if difference < 0:
        concatenated = hash1 + hash2
    else:
        concatenated = hash2 + hash1

    new_hash_lib = sha256()
    new_hash_lib.update(concatenated)
    new_digest = new_hash_lib.digest()
    return new_digest

完全なコード例を実行する

以下の完全なコード例を実行すると、前述のステップをすべて最初から最後まで実行します。

Java
import com.amazon.ion.IonBlob;
import com.amazon.ion.IonDatagram;
import com.amazon.ion.IonList;
import com.amazon.ion.IonReader;
import com.amazon.ion.IonString;
import com.amazon.ion.IonStruct;
import com.amazon.ion.IonSystem;
import com.amazon.ion.IonValue;
import com.amazon.ion.system.IonSystemBuilder;
import com.amazonaws.services.qldb.AmazonQLDB;
import com.amazonaws.services.qldb.AmazonQLDBClientBuilder;
import com.amazonaws.services.qldb.model.GetBlockRequest;
import com.amazonaws.services.qldb.model.GetBlockResult;
import com.amazonaws.services.qldb.model.GetDigestRequest;
import com.amazonaws.services.qldb.model.GetDigestResult;
import com.amazonaws.services.qldb.model.GetRevisionRequest;
import com.amazonaws.services.qldb.model.GetRevisionResult;
import com.amazonaws.services.qldb.model.ValueHolder;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.ListIterator;

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.qldbsession.QldbSessionClient;
import software.amazon.awssdk.services.qldbsession.QldbSessionClientBuilder;
import software.amazon.qldb.QldbDriver;
import software.amazon.qldb.Result;

public class BlockHashVerification {
    private static final IonSystem SYSTEM = IonSystemBuilder.standard().build();
    private static final QldbDriver driver = createQldbDriver();
    private static final AmazonQLDB client = AmazonQLDBClientBuilder.standard().build();
    private static final String region = "us-east-1";
    private static final String ledgerName = "vehicle-registration";
    private static final String tableName = "VehicleRegistration";
    private static final String vin = "KM8SRDHF6EU074761";
    private static final int HASH_LENGTH = 32;

    /**
     * Create a pooled driver for creating sessions.
     *
     * @return The pooled driver for creating sessions.
     */
    public static QldbDriver createQldbDriver() {
        QldbSessionClientBuilder sessionClientBuilder = QldbSessionClient.builder();
        sessionClientBuilder.region(Region.of(region));

        return QldbDriver.builder()
                .ledger(ledgerName)
                .sessionClientBuilder(sessionClientBuilder)
                .build();
    }

    /**
     * Takes two hashes, sorts them, concatenates them, and then returns the
     * hash of the concatenated array.
     *
     * @param h1
     *              Byte array containing one of the hashes to compare.
     * @param h2
     *              Byte array containing one of the hashes to compare.
     * @return the concatenated array of hashes.
     */
    public static byte[] dot(final byte[] h1, final byte[] h2) {
        if (h1.length != HASH_LENGTH || h2.length != HASH_LENGTH) {
            throw new IllegalArgumentException("Invalid hash.");
        }

        int byteEqual = 0;
        for (int i = h1.length - 1; i >= 0; i--) {
            byteEqual = Byte.compare(h1[i], h2[i]);
            if (byteEqual != 0) {
                break;
            }
        }

        byte[] concatenated = new byte[h1.length + h2.length];
        if (byteEqual < 0) {
            System.arraycopy(h1, 0, concatenated, 0, h1.length);
            System.arraycopy(h2, 0, concatenated, h1.length, h2.length);
        } else {
            System.arraycopy(h2, 0, concatenated, 0, h2.length);
            System.arraycopy(h1, 0, concatenated, h2.length, h1.length);
        }

        MessageDigest messageDigest;
        try {
            messageDigest = MessageDigest.getInstance("SHA-256");
        } catch (NoSuchAlgorithmException e) {
            throw new IllegalStateException("SHA-256 message digest is unavailable", e);
        }

        messageDigest.update(concatenated);
        return messageDigest.digest();
    }

    public static void main(String[] args) {
        // Get a digest
        GetDigestRequest digestRequest = new GetDigestRequest().withName(ledgerName);
        GetDigestResult digestResult = client.getDigest(digestRequest);

        java.nio.ByteBuffer digest = digestResult.getDigest();

        // expectedDigest is the buffer we will use later to compare against our calculated digest
        byte[] expectedDigest = new byte[digest.remaining()];
        digest.get(expectedDigest);

        // Retrieve info for the given vin's document revisions
        Result result = driver.execute(txn -> {
            final String query = String.format("SELECT blockAddress, hash, metadata.id FROM _ql_committed_%s WHERE data.VIN = '%s'", tableName, vin);
            return txn.execute(query);
        });

        System.out.printf("Verifying document revisions for vin '%s' in table '%s' in ledger '%s'%n", vin, tableName, ledgerName);

        for (IonValue ionValue : result) {
            IonStruct ionStruct = (IonStruct)ionValue;

            // Get the requested fields
            IonValue blockAddress = ionStruct.get("blockAddress");
            IonBlob hash = (IonBlob)ionStruct.get("hash");
            String metadataId = ((IonString)ionStruct.get("id")).stringValue();

            System.out.printf("Verifying document revision for id '%s'%n", metadataId);

            String blockAddressText = blockAddress.toString();

            // Submit a request for the revision
            GetRevisionRequest revisionRequest = new GetRevisionRequest()
                    .withName(ledgerName)
                    .withBlockAddress(new ValueHolder().withIonText(blockAddressText))
                    .withDocumentId(metadataId)
                    .withDigestTipAddress(digestResult.getDigestTipAddress());

            // Get a result back
            GetRevisionResult revisionResult = client.getRevision(revisionRequest);

            String proofText = revisionResult.getProof().getIonText();

            // Take the proof and convert it to a list of byte arrays
            List<byte[]> internalHashes = new ArrayList<>();
            IonReader reader = SYSTEM.newReader(proofText);
            reader.next();
            reader.stepIn();
            while (reader.next() != null) {
                internalHashes.add(reader.newBytes());
            }

            // Calculate digest
            byte[] calculatedDigest = internalHashes.stream().reduce(hash.getBytes(), BlockHashVerification::dot);

            boolean verified = Arrays.equals(expectedDigest, calculatedDigest);

            if (verified) {
                System.out.printf("Successfully verified document revision for id '%s'!%n", metadataId);
            } else {
                System.out.printf("Document revision for id '%s' verification failed!%n", metadataId);
                return;
            }

            // Submit a request for the block
            GetBlockRequest getBlockRequest = new GetBlockRequest()
                    .withName(ledgerName)
                    .withBlockAddress(new ValueHolder().withIonText(blockAddressText))
                    .withDigestTipAddress(digestResult.getDigestTipAddress());

            // Get a result back
            GetBlockResult getBlockResult = client.getBlock(getBlockRequest);

            String blockText = getBlockResult.getBlock().getIonText();

            IonDatagram datagram = SYSTEM.getLoader().load(blockText);
            ionStruct = (IonStruct)datagram.get(0);

            final byte[] blockHash = ((IonBlob)ionStruct.get("blockHash")).getBytes();

            proofText = getBlockResult.getProof().getIonText();

            // Take the proof and create a list of hash binary data
            datagram = SYSTEM.getLoader().load(proofText);
            ListIterator<IonValue> listIter = ((IonList)datagram.iterator().next()).listIterator();

            internalHashes.clear();
            while (listIter.hasNext()) {
                internalHashes.add(((IonBlob)listIter.next()).getBytes());
            }

            // Calculate digest
            calculatedDigest = internalHashes.stream().reduce(blockHash, BlockHashVerification::dot);

            verified = Arrays.equals(expectedDigest, calculatedDigest);

            if (verified) {
                System.out.printf("Block address '%s' successfully verified!%n", blockAddressText);
            } else {
                System.out.printf("Block address '%s' verification failed!%n", blockAddressText);
            }
        }
    }
}
.NET
using Amazon.IonDotnet;
using Amazon.IonDotnet.Builders;
using Amazon.IonDotnet.Tree;
using Amazon.QLDB;
using Amazon.QLDB.Driver;
using Amazon.QLDB.Model;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;

namespace BlockHashVerification
{
    class BlockHashVerification
    {
        private static readonly string ledgerName = "vehicle-registration";
        private static readonly string tableName = "VehicleRegistration";
        private static readonly string vin = "KM8SRDHF6EU074761";
        private static readonly IQldbDriver driver = QldbDriver.Builder().WithLedger(ledgerName).Build();
        private static readonly IAmazonQLDB client = new AmazonQLDBClient();

        /// <summary>
        /// Takes two hashes, sorts them, concatenates them, and then returns the
        /// hash of the concatenated array.
        /// </summary>
        /// <param name="h1">Byte array containing one of the hashes to compare.</param>
        /// <param name="h2">Byte array containing one of the hashes to compare.</param>
        /// <returns>The concatenated array of hashes.</returns>
        private static byte[] Dot(byte[] h1, byte[] h2)
        {
            if (h1.Length == 0)
            {
                return h2;
            }

            if (h2.Length == 0)
            {
                return h1;
            }

            HashAlgorithm hashAlgorithm = HashAlgorithm.Create("SHA256");
            HashComparer comparer = new HashComparer();
            if (comparer.Compare(h1, h2) < 0)
            {
                return hashAlgorithm.ComputeHash(h1.Concat(h2).ToArray());
            }
            else
            {
                return hashAlgorithm.ComputeHash(h2.Concat(h1).ToArray());
            }
        }

        private class HashComparer : IComparer<byte[]>
        {
            private static readonly int HASH_LENGTH = 32;

            public int Compare(byte[] h1, byte[] h2)
            {
                if (h1.Length != HASH_LENGTH || h2.Length != HASH_LENGTH)
                {
                    throw new ArgumentException("Invalid hash");
                }

                for (var i = h1.Length - 1; i >= 0; i--)
                {
                    var byteEqual = (sbyte)h1[i] - (sbyte)h2[i];
                    if (byteEqual != 0)
                    {
                        return byteEqual;
                    }
                }

                return 0;
            }
        }

        static void Main()
        {
            // Get a digest
            GetDigestRequest getDigestRequest = new GetDigestRequest
            {
                Name = ledgerName
            };
            GetDigestResponse getDigestResponse = client.GetDigestAsync(getDigestRequest).Result;

            // expectedDigest is the buffer we will use later to compare against our calculated digest
            MemoryStream digest = getDigestResponse.Digest;
            byte[] expectedDigest = digest.ToArray();

            // Retrieve info for the given vin's document revisions
            var result = driver.Execute(txn => {
                string query = $"SELECT blockAddress, hash, metadata.id FROM _ql_committed_{tableName} WHERE data.VIN = '{vin}'";
                return txn.Execute(query);
            });

            Console.WriteLine($"Verifying document revisions for vin '{vin}' in table '{tableName}' in ledger '{ledgerName}'");

            foreach (IIonValue ionValue in result)
            {
                IIonStruct ionStruct = ionValue;

                // Get the requested fields
                IIonValue blockAddress = ionStruct.GetField("blockAddress");
                IIonBlob hash = ionStruct.GetField("hash");
                String metadataId = ionStruct.GetField("id").StringValue;

                Console.WriteLine($"Verifying document revision for id '{metadataId}'");

                // Use an Ion Reader to convert block address to text
                IIonReader reader = IonReaderBuilder.Build(blockAddress);
                StringWriter sw = new StringWriter();
                IIonWriter textWriter = IonTextWriterBuilder.Build(sw);
                textWriter.WriteValues(reader);
                string blockAddressText = sw.ToString();

                // Submit a request for the revision
                GetRevisionRequest revisionRequest = new GetRevisionRequest
                {
                    Name = ledgerName,
                    BlockAddress = new ValueHolder
                    {
                        IonText = blockAddressText
                    },
                    DocumentId = metadataId,
                    DigestTipAddress = getDigestResponse.DigestTipAddress
                };
                
                // Get a response back
                GetRevisionResponse revisionResponse = client.GetRevisionAsync(revisionRequest).Result;

                string proofText = revisionResponse.Proof.IonText;
                IIonDatagram proofValue = IonLoader.Default.Load(proofText);

                byte[] documentHash = hash.Bytes().ToArray();
                foreach (IIonValue proofHash in proofValue.GetElementAt(0))
                {
                    // Calculate the digest
                    documentHash = Dot(documentHash, proofHash.Bytes().ToArray());
                }

                bool verified = expectedDigest.SequenceEqual(documentHash);

                if (verified)
                {
                    Console.WriteLine($"Successfully verified document revision for id '{metadataId}'!");
                }
                else
                {
                    Console.WriteLine($"Document revision for id '{metadataId}' verification failed!");
                    return;
                }

                // Submit a request for the block
                GetBlockRequest getBlockRequest = new GetBlockRequest
                {
                    Name = ledgerName,
                    BlockAddress = new ValueHolder
                    {
                        IonText = blockAddressText
                    },
                    DigestTipAddress = getDigestResponse.DigestTipAddress
                };

                // Get a response back
                GetBlockResponse getBlockResponse = client.GetBlockAsync(getBlockRequest).Result;

                string blockText = getBlockResponse.Block.IonText;
                IIonDatagram blockValue = IonLoader.Default.Load(blockText);

                // blockValue is a IonDatagram, and the first value is an IonStruct containing the blockHash
                byte[] blockHash = blockValue.GetElementAt(0).GetField("blockHash").Bytes().ToArray();

                proofText = getBlockResponse.Proof.IonText;
                proofValue = IonLoader.Default.Load(proofText);

                foreach (IIonValue proofHash in proofValue.GetElementAt(0))
                {
                    // Calculate the digest
                    blockHash = Dot(blockHash, proofHash.Bytes().ToArray());
                }

                verified = expectedDigest.SequenceEqual(blockHash);

                if (verified)
                {
                    Console.WriteLine($"Block address '{blockAddressText}' successfully verified!");
                }
                else
                {
                    Console.WriteLine($"Block address '{blockAddressText}' verification failed!");
                }
            }
        }
    }
}
Go
package main

import (
    "context"
    "crypto/sha256"
    "errors"
    "fmt"
    "reflect"

    "github.com/amzn/ion-go/ion"
    "github.com/aws/aws-sdk-go/aws"
    AWSSession "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/qldb"
    "github.com/aws/aws-sdk-go/service/qldbsession"
    "github.com/awslabs/amazon-qldb-driver-go/qldbdriver"
)

const (
    hashLength = 32
    ledgerName = "vehicle-registration"
    tableName  = "VehicleRegistration"
    vin        = "KM8SRDHF6EU074761"
)

// Takes two hashes, sorts them, concatenates them, and then returns the hash of the concatenated array.
func dot(h1, h2 []byte) ([]byte, error) {
    compare, err := hashComparator(h1, h2)
    if err != nil {
        return nil, err
    }

    var concatenated []byte
    if compare < 0 {
        concatenated = append(h1, h2...)
    } else {
        concatenated = append(h2, h1...)
    }

    newHash := sha256.Sum256(concatenated)
    return newHash[:], nil
}

func hashComparator(h1 []byte, h2 []byte) (int16, error) {
    if len(h1) != hashLength || len(h2) != hashLength {
        return 0, errors.New("invalid hash")
    }
    for i := range h1 {
        // Reverse index for little endianness
        index := hashLength - 1 - i

        // Handle byte being unsigned and overflow
        h1Int := int16(h1[index])
        h2Int := int16(h2[index])
        if h1Int > 127 {
            h1Int = 0 - (256 - h1Int)
        }
        if h2Int > 127 {
            h2Int = 0 - (256 - h2Int)
        }

        difference := h1Int - h2Int
        if difference != 0 {
            return difference, nil
        }
    }
    return 0, nil
}

func main() {
    driverSession := AWSSession.Must(AWSSession.NewSession(aws.NewConfig()))
    qldbSession := qldbsession.New(driverSession)
    driver, err := qldbdriver.New(ledgerName, qldbSession, func(options *qldbdriver.DriverOptions) {})
    if err != nil {
        panic(err)
    }
    client := qldb.New(driverSession)

    // Get a digest
    currentLedgerName := ledgerName
    input := qldb.GetDigestInput{Name: &currentLedgerName}
    digestOutput, err := client.GetDigest(&input)
    if err != nil {
        panic(err)
    }

    // expectedDigest is the buffer we will later use to compare against our calculated digest
    expectedDigest := digestOutput.Digest

    // Retrieve info for the given vin's document revisions
    result, err := driver.Execute(context.Background(), func(txn qldbdriver.Transaction) (interface{}, error) {
        statement := fmt.Sprintf(
                "SELECT blockAddress, hash, metadata.id FROM _ql_committed_%s WHERE data.VIN = '%s'",
                tableName,
                vin)
        result, err := txn.Execute(statement)
        if err != nil {
            return nil, err
        }

        results := make([]map[string]interface{}, 0)

        // Convert the result set into a map
        for result.Next(txn) {
            var doc map[string]interface{}
            err := ion.Unmarshal(result.GetCurrentData(), &doc)
            if err != nil {
                return nil, err
            }
            results = append(results, doc)
        }
        return results, nil
    })
    if err != nil {
        panic(err)
    }
    resultSlice := result.([]map[string]interface{})

    fmt.Printf("Verifying document revisions for vin '%s' in table '%s' in ledger '%s'\n", vin, tableName, ledgerName)

    for _, value := range resultSlice {
        // Get the requested fields
        ionBlockAddress, err := ion.MarshalText(value["blockAddress"])
        if err != nil {
            panic(err)
        }
        blockAddress := string(ionBlockAddress)
        metadataId := value["id"].(string)
        documentHash := value["hash"].([]byte)

        fmt.Printf("Verifying document revision for id '%s'\n", metadataId)

        // Submit a request for the revision
        revisionInput := qldb.GetRevisionInput{
            BlockAddress:     &qldb.ValueHolder{IonText: &blockAddress},
            DigestTipAddress: digestOutput.DigestTipAddress,
            DocumentId:       &metadataId,
            Name:             &currentLedgerName,
        }

        // Get a result back
        revisionOutput, err := client.GetRevision(&revisionInput)
        if err != nil {
            panic(err)
        }

        proofText := revisionOutput.Proof.IonText

        // Use ion.Reader to iterate over the proof's node hashes
        reader := ion.NewReaderString(*proofText)
        // Enter the struct containing node hashes
        reader.Next()
        if err := reader.StepIn(); err != nil {
            panic(err)
        }

        // Going through nodes and calculate digest
        for reader.Next() {
            val, _ := reader.ByteValue()
            documentHash, err = dot(documentHash, val)
        }

        // Compare documentHash with the expected digest
        verified := reflect.DeepEqual(documentHash, expectedDigest)

        if verified {
            fmt.Printf("Successfully verified document revision for id '%s'!\n", metadataId)
        } else {
            fmt.Printf("Document revision for id '%s' verification failed!\n", metadataId)
            return
        }

        // Submit a request for the block
        blockInput := qldb.GetBlockInput{
            Name:             &currentLedgerName,
            BlockAddress:     &qldb.ValueHolder{IonText: &blockAddress},
            DigestTipAddress: digestOutput.DigestTipAddress,
        }

        // Get a result back
        blockOutput, err := client.GetBlock(&blockInput)
        if err != nil {
            panic(err)
        }

        proofText = blockOutput.Proof.IonText

        block := new(map[string]interface{})
        err = ion.UnmarshalString(*blockOutput.Block.IonText, block)
        if err != nil {
            panic(err)
        }

        blockHash := (*block)["blockHash"].([]byte)

        // Use ion.Reader to iterate over the proof's node hashes
        reader = ion.NewReaderString(*proofText)
        // Enter the struct containing node hashes
        reader.Next()
        if err := reader.StepIn(); err != nil {
            panic(err)
        }

        // Going through nodes and calculate digest
        for reader.Next() {
            val, err := reader.ByteValue()
            if err != nil {
                panic(err)
            }
            blockHash, err = dot(blockHash, val)
        }

        // Compare blockHash with the expected digest
        verified = reflect.DeepEqual(blockHash, expectedDigest)

        if verified {
            fmt.Printf("Block address '%s' successfully verified!\n", blockAddress)
        } else {
            fmt.Printf("Block address '%s' verification failed!\n", blockAddress)
            return
        }
    }
}
Node.js
import { QldbDriver, Result, TransactionExecutor} from "amazon-qldb-driver-nodejs";
import { QLDB } from "aws-sdk"
import { GetBlockRequest, GetBlockResponse, GetDigestRequest, GetDigestResponse, GetRevisionRequest, GetRevisionResponse } from "aws-sdk/clients/qldb";
import { createHash } from "crypto";
import { dom, dumpText, load } from "ion-js"

const ledgerName: string = "vehicle-registration";
const tableName: string = "VehicleRegistration";
const vin: string = "KM8SRDHF6EU074761";
const driver: QldbDriver = new QldbDriver(ledgerName);
const qldbClient: QLDB = new QLDB();
const HASH_SIZE = 32;

/**
 * Takes two hashes, sorts them, concatenates them, and calculates a digest based on the concatenated hash.
 * @param h1 Byte array containing one of the hashes to compare.
 * @param h2 Byte array containing one of the hashes to compare.
 * @returns The digest calculated from the concatenated hash values.
 */
function dot(h1: Uint8Array, h2: Uint8Array): Uint8Array {
    if (h1.length === 0) {
        return h2;
    }
    if (h2.length === 0) {
        return h1;
    }

    const newHashLib = createHash("sha256");

    let concatenated: Uint8Array;
    if (hashComparator(h1, h2) < 0) {
        concatenated = concatenate(h1, h2);
    } else {
        concatenated = concatenate(h2, h1);
    }
    newHashLib.update(concatenated);
    return newHashLib.digest();
}

/**
 * Compares two hashes by their **signed** byte values in little-endian order.
 * @param hash1 The hash value to compare.
 * @param hash2 The hash value to compare.
 * @returns Zero if the hash values are equal, otherwise return the difference of the first pair of non-matching
 *          bytes.
 * @throws RangeError When the hash is not the correct hash size.
 */
function hashComparator(hash1: Uint8Array, hash2: Uint8Array): number {
    if (hash1.length !== HASH_SIZE || hash2.length !== HASH_SIZE) {
        throw new RangeError("Invalid hash.");
    }
    for (let i = hash1.length-1; i >= 0; i--) {
        const difference: number = (hash1[i]<<24 >>24) - (hash2[i]<<24 >>24);
        if (difference !== 0) {
            return difference;
        }
    }
    return 0;
}

/**
 * Helper method that concatenates two Uint8Array.
 * @param arrays List of arrays to concatenate, in the order provided.
 * @returns The concatenated array.
 */
function concatenate(...arrays: Uint8Array[]): Uint8Array {
    let totalLength = 0;
    for (const arr of arrays) {
        totalLength += arr.length;
    }
    const result = new Uint8Array(totalLength);
    let offset = 0;
    for (const arr of arrays) {
        result.set(arr, offset);
        offset += arr.length;
    }
    return result;
}

/**
 * Helper method that checks for equality between two Uint8Array.
 * @param expected Byte array containing one of the hashes to compare.
 * @param actual Byte array containing one of the hashes to compare.
 * @returns Boolean indicating equality between the two Uint8Array.
 */
function isEqual(expected: Uint8Array, actual: Uint8Array): boolean {
    if (expected === actual) return true;
    if (expected == null || actual == null) return false;
    if (expected.length !== actual.length) return false;

    for (let i = 0; i < expected.length; i++) {
        if (expected[i] !== actual[i]) {
            return false;
        }
    }
    return true;
}

const main = async function (): Promise<void> {
    // Get a digest
    const getDigestRequest: GetDigestRequest = {
        Name: ledgerName
    };
    const getDigestResponse: GetDigestResponse = await qldbClient.getDigest(getDigestRequest).promise();

    // expectedDigest is the buffer we will later use to compare against our calculated digest
    const expectedDigest: Uint8Array = <Uint8Array>getDigestResponse.Digest;

    const result: dom.Value[] = await driver.executeLambda(async (txn: TransactionExecutor): Promise<dom.Value[]> => {
        const query: string = `SELECT blockAddress, hash, metadata.id FROM _ql_committed_${tableName} WHERE data.VIN = '${vin}'`;
        const queryResult: Result = await txn.execute(query);
        return queryResult.getResultList();
    });

    console.log(`Verifying document revisions for vin '${vin}' in table '${tableName}' in ledger '${ledgerName}'`);

    for (let value of result) {
        // Get the requested fields
        const blockAddress: dom.Value = value.get("blockAddress");
        const hash: dom.Value = value.get("hash");
        const metadataId: string = value.get("id").stringValue();

        console.log(`Verifying document revision for id '${metadataId}'`);

        // Submit a request for the revision
        const revisionRequest: GetRevisionRequest = {
            Name: ledgerName,
            BlockAddress: {
                IonText: dumpText(blockAddress)
            },
            DocumentId: metadataId,
            DigestTipAddress: getDigestResponse.DigestTipAddress
        };

        // Get a response back
        const revisionResponse: GetRevisionResponse = await qldbClient.getRevision(revisionRequest).promise();

        let proofValue: dom.Value = load(revisionResponse.Proof.IonText);

        let documentHash: Uint8Array = hash.uInt8ArrayValue();
        proofValue.elements().forEach((proofHash: dom.Value) => {
            // Calculate the digest
            documentHash = dot(documentHash, proofHash.uInt8ArrayValue());
        });

        let verified: boolean = isEqual(expectedDigest, documentHash);

        if (verified) {
            console.log(`Successfully verified document revision for id '${metadataId}'!`);
        } else {
            console.log(`Document revision for id '${metadataId}' verification failed!`);
            return;
        }

        // Submit a request for the block
        const getBlockRequest: GetBlockRequest = {
            Name: ledgerName,
            BlockAddress: {
                IonText: dumpText(blockAddress)
            },
            DigestTipAddress: getDigestResponse.DigestTipAddress
        };

        // Get a response back
        const getBlockResponse: GetBlockResponse = await qldbClient.getBlock(getBlockRequest).promise();

        const blockValue: dom.Value = load(getBlockResponse.Block.IonText)
        let blockHash: Uint8Array = blockValue.get("blockHash").uInt8ArrayValue();

        proofValue = load(getBlockResponse.Proof.IonText);

        proofValue.elements().forEach((proofHash: dom.Value) => {
            // Calculate the digest
            blockHash = dot(blockHash, proofHash.uInt8ArrayValue());
        });

        verified = isEqual(expectedDigest, blockHash);

        if (verified) {
            console.log(`Block address '${dumpText(blockAddress)}' successfully verified!`);
        } else {
            console.log(`Block address '${dumpText(blockAddress)}' verification failed!`);
        }
    }
};

if (require.main === module) {
    main();
}
Python
from amazon.ion.simpleion import dumps, loads
from array import array
from boto3 import client
from functools import reduce
from hashlib import sha256
from pyqldb.driver.qldb_driver import QldbDriver

ledger_name = 'vehicle-registration'
table_name = 'VehicleRegistration'
vin = 'KM8SRDHF6EU074761'
qldb_client = client('qldb')
hash_length = 32


def query_doc_revision(txn):
    query = "SELECT blockAddress, hash, metadata.id FROM _ql_committed_{} WHERE data.VIN = '{}'".format(table_name, vin)
    return txn.execute_statement(query)


def block_address_to_dictionary(ion_dict):
    """
    Convert a block address from IonPyDict into a dictionary.
    Shape of the dictionary must be: {'IonText': "{strandId: <"strandId">, sequenceNo: <sequenceNo>}"}

    :type ion_dict: :py:class:`amazon.ion.simple_types.IonPyDict`/str
    :param ion_dict: The block address value to convert.

    :rtype: dict
    :return: The converted dict.
    """
    block_address = {'IonText': {}}
    if not isinstance(ion_dict, str):
        py_dict = '{{strandId: "{}", sequenceNo:{}}}'.format(ion_dict['strandId'], ion_dict['sequenceNo'])
        ion_dict = py_dict
    block_address['IonText'] = ion_dict
    return block_address


def dot(hash1, hash2):
    """
    Takes two hashes, sorts them, concatenates them, and then returns the
    hash of the concatenated array.

    :type hash1: bytes
    :param hash1: The hash value to compare.

    :type hash2: bytes
    :param hash2: The hash value to compare.

    :rtype: bytes
    :return: The new hash value generated from concatenated hash values.
    """
    if len(hash1) != hash_length or len(hash2) != hash_length:
        raise ValueError('Illegal hash.')

    hash_array1 = array('b', hash1)
    hash_array2 = array('b', hash2)

    difference = 0
    for i in range(len(hash_array1) - 1, -1, -1):
        difference = hash_array1[i] - hash_array2[i]
        if difference != 0:
            break

    if difference < 0:
        concatenated = hash1 + hash2
    else:
        concatenated = hash2 + hash1

    new_hash_lib = sha256()
    new_hash_lib.update(concatenated)
    new_digest = new_hash_lib.digest()
    return new_digest


# Get a digest
get_digest_response = qldb_client.get_digest(Name=ledger_name)

# expected_digest is the buffer we will later use to compare against our calculated digest
expected_digest = get_digest_response.get('Digest')
digest_tip_address = get_digest_response.get('DigestTipAddress')

qldb_driver = QldbDriver(ledger_name=ledger_name)

# Retrieve info for the given vin's document revisions
result = qldb_driver.execute_lambda(query_doc_revision)

print("Verifying document revisions for vin '{}' in table '{}' in ledger '{}'".format(vin, table_name, ledger_name))

for value in result:
    # Get the requested fields
    block_address = value['blockAddress']
    document_hash = value['hash']
    metadata_id = value['id']

    print("Verifying document revision for id '{}'".format(metadata_id))

    # Submit a request for the revision and get a result back
    proof_response = qldb_client.get_revision(Name=ledger_name,
                                              BlockAddress=block_address_to_dictionary(block_address),
                                              DocumentId=metadata_id,
                                              DigestTipAddress=digest_tip_address)

    proof_text = proof_response.get('Proof').get('IonText')
    proof_hashes = loads(proof_text)

    # Calculate digest
    calculated_digest = reduce(dot, proof_hashes, document_hash)

    verified = calculated_digest == expected_digest
    if verified:
        print("Successfully verified document revision for id '{}'!".format(metadata_id))
    else:
        print("Document revision for id '{}' verification failed!".format(metadata_id))

    # Submit a request for the block and get a result back
    block_response = qldb_client.get_block(Name=ledger_name, BlockAddress=block_address_to_dictionary(block_address),
                                           DigestTipAddress=digest_tip_address)

    block_text = block_response.get('Block').get('IonText')
    block = loads(block_text)

    block_hash = block.get('blockHash')

    proof_text = block_response.get('Proof').get('IonText')
    proof_hashes = loads(proof_text)

    # Calculate digest
    calculated_digest = reduce(dot, proof_hashes, block_hash)

    verified = calculated_digest == expected_digest
    if verified:
        print("Block address '{}' successfully verified!".format(dumps(block_address,
                                                                       binary=False,
                                                                       omit_version_marker=True)))
    else:
        print("Block address '{}' verification failed!".format(block_address))