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TLS-SRP-SHA-WITH-AES-256-CBC-SHA Cipher Suite
A breakdown of the Cipher Suite TLS_SRP_SHA_WITH_AES_256_CBC_SHA, its strengths, and its weaknesses.
Cipher
Advanced Encryption Standard - AES
Grade - A
AES should be used in cipher suites because it offers strong security with efficient performance, large block size (128 bits), and resistance to known attacks. Its widespread adoption and thorough analysis by the cryptographic community ensure reliability and robustness for encrypting sensitive data.
Hash
Secure Hash Algorithm - SHA
Grade - D
Chosen prefix attacks for SHA1 are feasible at an accessible cost to a well-funded adversary. This level of expense, while significant, does not pose a substantial barrier to attackers with sufficient resources, making such attacks a credible threat.
Cipher Mode
Cipher Block Chaining - CBC
Grade - D
Cipher Block Chaining (CBC) mode is vulnerable to the Lucky13 and POODLE (in TLS v1.2 and below) attacks. The Lucky13 attack exploits timing discrepancies in padding validation, allowing attackers to gradually reveal plaintext. The POODLE attack leverages padding errors to decrypt ciphertext by repeatedly modifying and sending it to the server, observing the error responses. These vulnerabilities arise from CBC’s handling of padding and error messages, making it less secure than modern encryption modes like Galois Counter Mode (GCM), which offer stronger integrity and confidentiality guarantees.
