v4.5.0 - Marseille

New features

• Added the mode MODE_GCM_SIV to Crypto.Cipher.AES (AES-GCM-SIV, RFC 8452),
  for authenticated encryption that is resistant to the reuse of a nonce.
• Added the mode MODE_XTS to Crypto.Cipher.AES (IEEE 1619, NIST SP 800-38E),
  for the encryption of storage.
• CTR mode is about 35% faster on short bytes messages.

Breaking changes

• export_key of RSA and DSA keys raises ValueError for a private key in the 'OpenSSH' format,
  like ECC keys. It used to silently return the public key, ignoring any passphrase.
  To export the public key, use key.public_key().export_key('OpenSSH').

Resolved issues

• Security: the base64 body of a PEM block (for instance, a private key that is not encrypted)
  was decoded with binascii.a2b_base64, which looks up each character in a table, and could leak
  the key through a cache side channel. The body is now decoded in constant time, and it is no longer
  processed by Python string functions that look up characters in a table. Thanks to Li-Chung Chiang.