Does TLS use CBC?
The SSL/TLS connection must use one of the block encryption ciphers that use CBC modes, such as DES or AES. Since the connection is terminated each time, the SSL/TLS client must be able to continue to reestablish the SSL/TLS channel long enough for the message to be decrypted.
What is TLS CBC?
There are several block cipher modes, but the one that was originally standardized in SSL (and continues to be used in TLS) is Cipher Block Chaining (CBC). In CBC, the plaintext of one block is combined with the ciphertext of the previous block using the exclusive OR operation (XOR). CBC has some nice properties.
Can a AEAD cipher be used with TLS 1.2?
Because of this, AEAD can be used with TLS 1.2 and with TLS 1.3 only AEAD Cipher suits will work. Technically in TLS the steam ciphers with CHACHA20_POLY1305 with ECDHE Key exchange (TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 and TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256) will work.
Why is CBC vulnerable in TLS 1.3?
TLS 1.3 is a reboot of the TLS protocol which focused on up to date cryptography rather than backwards compatibility. Now CBC is not as secure as you make it to be, and the way that it was used in TLS made it particularly vulnerable. To note: in TLS the HMAC authentication tag was created over the plaintext rather than the ciphertext.
What’s the difference between CBC and GCM in TLS?
CBC is an encryption mode only: it provides confidentiality, but not authenticity or integrity. You need to authenticate the data separately. It can be done, of course, and that was the only way to do it before TLS 1.2. But it’s hard to get right, which is why authenticated encryption modes are recommended. TLS 1.3 pushes GCM instead of CBC + HMAC.
Why is TLS prone to decryption oracle attacks?
Padding Oracle attacks; as originally designed in SSL (and carried into TLS 1.2), the way TLS implements CBC mode (with the padding and the HMAC) is prone to various decryption oracle attacks (where the attacker modifies the TLS record, and watches how the decryptor reacts).