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TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA Cipher Suite
A breakdown of the Cipher Suite TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA, its strengths, and its weaknesses.
Key Exchange Mechanism
Elliptic Curve Diffie Hellman Ephemeral - ECDHE
Grade - A
ECDHE (Elliptic Curve Diffie-Hellman Ephemeral) is used because it enhances security through the use of ephemeral keys, which are temporary and unique for each session. This ensures that even if one session’s key is compromised, past and future sessions remain secure. ECDHE provides perfect forward secrecy, meaning that the compromise of long-term keys does not affect the confidentiality of past communications. The ephemeral nature of the keys significantly reduces the risk of long-term data breaches and enhances the overall robustness of the cryptographic protocol.
Authentication
Elliptic Curve Digital Signature Algorithm - ECDSA
Grade - A
ECDSA (Elliptic Curve Digital Signature Algorithm) is used in cipher suites for authentication and integrity verification. Its efficiency in generating and verifying digital signatures makes it suitable for secure communication protocols like TLS, ensuring data confidentiality and integrity during exchanges over networks.
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.
