Known issues for the PKCS #11 library for AWS CloudHSM

The following issues impact the PKCS #11 library for AWS CloudHSM.

Issue: AES key wrap in version 3.0.0 of the PKCS #11 library does not validate IVs before use

If you specify an IV shorter than 8 bytes in length, it is padded with unpredictable bytes before use.

Note

This impacts C_WrapKey with CKM_AES_KEY_WRAP mechanism only.

• Impact: If you provide an IV that is shorter than 8 bytes in version 3.0.0 of PKCS #11 library, you may be unable to unwrap the key.

• Workarounds:

  • We strongly recommend you upgrade to version 3.0.1 or higher of the PKCS #11 library, which properly enforces IV length during AES key wrap. Amend your wrapping code to pass a NULL IV, or specify the default IV of 0xA6A6A6A6A6A6A6A6. For more information, see Custom IVs with Non-Compliant Length for AES Key Wrap.

  • If you wrapped any keys with version 3.0.0 of the PKCS #11 library using an IV shorter than 8 bytes, reach out to us for support.

• Resolution status: This issue has been resolved in version 3.0.1 of the PKCS #11 library. To wrap keys using AES key wrap, specify an IV that is NULL or 8 bytes long.

Issue: PKCS#11 SDK 2.0.4 and earlier versions always used the default IV of 0xA6A6A6A6A6A6A6A6 for AES key wrap and unwrap

User-provided IVs were silently ignored.

Note

This impacts C_WrapKey with CKM_AES_KEY_WRAP mechanism only.

• Impact:

  • If you used PKCS#11 SDK 2.0.4 or an earlier version and a user-provided IV, your keys are wrapped with the default IV of 0xA6A6A6A6A6A6A6A6.

  • If you used PKCS#11 SDK 3.0.0 or later and a user-provided IV, your keys are wrapped with the user-provided IV.

• Workarounds:

  • To unwrap keys wrapped with PKCS#11 SDK 2.0.4 or earlier use the default IV of 0xA6A6A6A6A6A6A6A6.

  • To unwrap keys wrapped with PKCS#11 SDK 3.0.0 or later, use the user-provided IV.

• Resolution status: We strongly recommend that you amend your wrapping and unwrapping code to pass a NULL IV, or specify the default IV of 0xA6A6A6A6A6A6A6A6.

Issue: The CKA_DERIVE attribute was not supported and was not handled

• Resolution status: We have implemented fixes to accept CKA_DERIVE if it is set to FALSE. CKA_DERIVE set to TRUE will not be supported until we begin to add key derivation function support to AWS CloudHSM. You must update your client and SDK(s) to version 1.1.1 or higher to benefit from the fix.

Issue: The CKA_SENSITIVE attribute was not supported and was not handled

• Resolution status: We have implemented fixes to accept and properly honor the CKA_SENSITIVE attribute. You must update your client and SDK(s) to version 1.1.1 or higher to benefit from the fix.

Issue: Multipart hashing and signing are not supported

• Impact: C_DigestUpdate and C_DigestFinal are not implemented. C_SignFinal is also not implemented and will fail with CKR_ARGUMENTS_BAD for a non-NULL buffer.

• Workaround: Hash your data within your application and use AWS CloudHSM only for signing the hash.

• Resolution status: We are fixing the client and the SDKs to correctly implement multipart hashing. Updates will be announced in the AWS CloudHSM forum and on the version history page.

Issue: C_GenerateKeyPair does not handle CKA_MODULUS_BITS or CKA_PUBLIC_EXPONENT in the private template in a manner that is compliant with standards

• Impact: C_GenerateKeyPair should return CKA_TEMPLATE_INCONSISTENT when the private template contains CKA_MODULUS_BITS or CKA_PUBLIC_EXPONENT. It instead generates a private key for which all usage fields are set to FALSE. The key cannot be used.

• Workaround: We recommend that your application check the usage field values in addition to the error code.

• Resolution status: We are implementing fixes to return the proper error message when an incorrect private key template is used. The updated PKCS #11 library will be announced on the version history page.

Issue: Buffers for the C_Encrypt and C_Decrypt API operations cannot exceed 16 KB when using the CKM_AES_GCM mechanism

AWS CloudHSM does not support multipart AES-GCM encryption.

• Impact: You cannot use the CKM_AES_GCM mechanism to encrypt data larger than 16 KB.

• Workaround: You can use an alternative mechanism such as CKM_AES_CBC , CKM_AES_CBC_PAD, or you can divide your data into pieces and encrypt each piece using AES_GCM individually. If you’re using AES_GCM, you must manage the division of your data and subsequent encryption. AWS CloudHSM does not perform multipart AES-GCM encryption for you. Note that FIPS requires that the initialization vector (IV) for AES-GCM be generated on the HSM. Therefore, the IV for each piece of your AES-GCM encrypted data will be different.

• Resolution status: We are fixing the SDK to fail explicitly if the data buffer is too large. We return CKR_MECHANISM_INVALID for the C_EncryptUpdate and C_DecryptUpdate API operations. We are evaluating alternatives to support larger buffers without relying on multipart encryption. Updates will be announced in the AWS CloudHSM forum and on the version history page.

Issue: Elliptic-curve Diffie-Hellman (ECDH) key derivation is executed partially within the HSM

Your EC private key remains within the HSM at all times, but the key derivation process is performed in multiple steps. As a result, intermediate results from each step are available on the client.

• Impact: In Client SDK 3, the key derived using the CKM_ECDH1_DERIVE mechanism is first available on the client and is then imported into the HSM. A key handle is then returned to your application.

• Workaround: If you are implementing SSL/TLS Offload in AWS CloudHSM, this limitation may not be an issue. If your application requires your key to remain within an FIPS boundary at all times, consider using an alternative protocol that does not rely on ECDH key derivation.

• Resolution status: We are developing the option to perform ECDH key derivation entirely within the HSM. The updated implementation will be announced on the version history page once available.

Issue: Verification of secp256k1 signatures fails on EL6 platforms such as CentOS6 and RHEL 6

This happens because the CloudHSM PKCS#11 library avoids a network call during initialization of the verification operation by using OpenSSL to verify EC curve data. Since Secp256k1 is not supported by the default OpenSSL package on EL6 platforms, the initialization fails.

• Impact: Secp256k1 signature verification will fail on EL6 platforms. The verify call will fail with a CKR_HOST_MEMORY error.

• Workaround: We recommend using either Amazon Linux 1 or any EL7 platform if your PKCS#11 application needs to verify secp256k1 signatures. Alternatively, upgrade to a version of the OpenSSL package that supports the secp256k1 curve.

• Resolution status: We are implementing fixes to fall back to the HSM if local curve validation is not available. The updated PKCS#11 library will be announced on the version history page.

Issue: Incorrect sequence of function calls gives undefined results instead of failing

• Impact: If you call an incorrect sequence of functions, the final result is incorrect even though the individual function calls return success. For instance, decrypted data may not match the original plaintext or signatures may fail to verify. This issue affects both single part and multi-part operations.

  Examples of incorrect function sequences:

  • C_EncryptInit/C_EncryptUpdate followed by C_Encrypt

  • C_DecryptInit/C_DecryptUpdate followed by C_Decrypt

  • C_SignInit/C_SignUpdate followed by C_Sign

  • C_VerifyInit/C_VerifyUpdate followed by C_Verify

  • C_FindObjectsInit followed by C_FindObjectsInit

• Workaround: Your application should, in compliance with the PKCS #11 specification, use the right sequence of function calls for both single and multi-part operations. Your application should not rely on the CloudHSM PKCS #11 library to return an error under this circumstance.

Issue: Read Only Session is not supported in SDK 5

• Issue: SDK 5 does not support opening Read-Only sessions with C_OpenSession.

• Impact: If you attempt to call C_OpenSession without providing CKF_RW_SESSION, the call will fail with the error CKR_FUNCTION_FAILED.

• Workaround: When opening a session, you must pass the CKF_SERIAL_SESSION | CKF_RW_SESSION flags to the C_OpenSession function call.

Issue: cryptoki.h header file is Windows-only

• Issue: With AWS CloudHSM Client SDK 5 versions 5.0.0 through 5.4.0 on Linux, the header file /opt/cloudhsm/include/pkcs11/cryptoki.h is only compatible with Windows operating systems.

• Impact: You may encounter issues when trying to include this header file in your application on Linux-based operating systems.

• Resolution status: Upgrade to AWS CloudHSM Client SDK 5 version 5.4.1 or above, which includes a Linux-compatible version of this header file.