Why is CBC mode insecure?
The reason the vulnerability exists is because block ciphers must have valid padding, and encryption algorithms will handle the padding for developers during encryption. Consequently, during development and testing, valid ciphertexts are used and developers may never even be aware padding exists.
Although CBC mode is more secure, its encryption is not tolerant of block losses. This is because blocks depend on their previous blocks for encryption. So, if block Bi is lost, the encryption of all subsequent blocks will not be possible.
CBC has some nice properties. The ciphertext produced by a block cipher is encrypted, so it (hopefully) looks random. In CBC, you're mixing this random looking encrypted data into the plaintext, making it very unlikely that there will be patterns in the output.
Not using a random initialization Vector (IV) with Cipher Block Chaining (CBC) Mode causes algorithms to be susceptible to dictionary attacks. CBC is the most commonly used mode of operation for a block cipher. It solves electronic code book's dictionary problems by XORing the ciphertext with plaintext.
ECB mode's issues arise from the fact that each block of the plaintext is encrypted completely independently. CBC mode eliminates this problem by carrying information from the encryption or decryption of one block to the next.
The CBC mode alone is susceptible to padding oracle attack.
By using this along with a single encryption key, organizations and individuals can safely encrypt and decrypt large amounts of plaintext. One of CBC's key characteristics is that it uses a chaining process that causes the decryption of a block of ciphertext to depend on all the preceding ciphertext blocks.
- Protocols: SSL2, SSL3, TLS1. 0 and TLS1. ...
- Encryption Ciphers: DES, 3DES, and RC4 (so only AES should be used) AES with CBC chaining mode (so only AES GCM should be used)
- Key Exchanges: RSA. DH key sizes < 2048. ECDH key size < 224.
AES-128-CBC is not broken but must be used correctly, nothing special just use of best practices.
AES-GCM is a more secure cipher than AES-CBC, because AES-CBC, operates by XOR'ing (eXclusive OR) each block with the previous block and cannot be written in parallel. This affects performance due to the complex mathematics involved requiring serial encryption.
Is CBC Mac collision resistant?
Using the same key for encryption and authentication
holds and thus the CBC-MAC tag is correct. This example also shows that a CBC-MAC cannot be used as a collision resistant one-way function: given a key it is trivial to create a different message which “hashes” to the same tag.
Some block cipher modes (CBC and PCBC essentially) for symmetric-key encryption algorithms require plain text input that is a multiple of the block size, so messages may have to be padded to bring them to this length.
The input to the encryption processes of the CBC, CFB, and OFB modes includes, in addition to the plaintext, a data block called the initialization vector (IV), denoted IV. The IV is used in an initial step in the encryption of a message and in the corresponding decryption of the message.
The AES-GCM mode of operation can actually be carried out in parallel both for encryption and decryption. The additional security that this method provides also allows the VPN to use only a 128-bit key, whereas AES-CBC typically requires a 256-bit key to be considered secure. CBC ciphers were removed in May of 2021.
The Advanced Encryption Standard, AES, is a symmetric encryption algorithm and one of the most secure.
