Amazon CloudFront
Developer Guide (API Version 2016-09-29)

Determining the Size of the Public Key in an SSL/TLS Certificate

When you're using CloudFront alternate domain names and HTTPS, the maximum size of the public key in an SSL/TLS certificate is 2048 bits. (This is the key size, not the number of characters in the public key.) If you use AWS Certificate Manager for your certificates, note that although ACM supports larger keys, you cannot use the larger keys with CloudFront.

You can determine the size of the public key by running the following OpenSSL command:

openssl x509 -in path and filename of SSL/TLS certificate -text -noout


  • -in specifies the path and filename of your SSL/TLS certificate.

  • -text causes OpenSSL to display the length of the public key in bits.

  • -noout prevents OpenSSL from displaying the public key.

Example output:

Public-Key: (2048 bit)