Knowledge Base

RSA (Rivest-Shamir-Adleman)

RSA^[443][444] key exchange is a key exchange^[133] that has no forward secrecy^{[127][128][129][130]}, and does not protect past sessions against future compromises. If long-term secret keys or passwords are compromised, encrypted communications and sessions recorded in the past can be retrieved and decrypted. Throughout its history RSA encryption has had many security flaws^{[445][446][447][448][449][450]} and was affected by variety of attack types: chosen-ciphertext attack^[55] (eg: Bleichenbacher's attack^[1][2], ROBOT attack^{[18][19][20][21]}), side-channel attack^[69][70][71] (eg: padding oracle attack^{[63][64][65][66]}, like Bleichenbacher's cat^[3][4][5][6]).

Always prefer cipher suites with PFS property over the non-PFS ones. Note that performance considerations implies preferring Ephemeral Elliptic-curve Diffie–Hellman^[432][433] over Ephemeral Diffie-Hellman^{[405][406][407][408]}.

RSA

Rivest–Shamir–Adleman^{[275][276][277]} is a digital signature^{[107][108][109][110]} algorithm, which is considered secure, however there are known weaknesses^{[278][279][280][281][282]}.

IDEA

Encryption algorithm International Data Encryption Algorithm^[355][356] is a block cipher^{[78][79][80][81]} which is considered secure^{[357][358][359]}, but leading client applications do not use this algorithm. Unless your application or requirements specifically call for their use, it is generally safer to avoid cipher suites that are not adopted and supported by a critical mass of the industry.

Remove the cipher suite from the list of cipher suites supported by your server.

CBC

Encryption mode is cipher block chaining^[28][29][30]. It is vulnerable^[31] to timing attack^[188] (eg: Lucky Thirteen attack^[11][12]) and padding oracle attack^{[63][64][65][66]} (eg: POODLE attack^[13][14][15]).

Remove the cipher suite from the list of cipher suites supported by your server or at least set the cipher suite order explicitly and any cipher suite modes be preferred over ciphers suites with CBC modes.

64

Any symmetric key^{[185][186][187]} with key size^[184] less than 128 bits are disallowed by National Institute of Standards and Technology^[470][471] as it is vulnerable to preimage attack^[67] in theory. It cannot reliably prove that message came from the stated sender (its authenticity) and has not been changed, so connection is open for a man-in-the-middle attack^[61].

Remove the cipher suite from the list of cipher suites supported by your server.

64

Any block cipher^{[78][79][80][81]} uses a block size^[87] of 64 bits is vulnerable to sweet32 attack^{[22][23][24][25]}.

Remove the cipher suite from the list of cipher suites supported by your server, or setup yout server to enforce changing session key regularly (rekeying^[174]).

SHA-1

message authentication code^{[135][136][137][138]} is a hashed message authentication code^{[139][140][141][142][143][144][145]} which is considered secure^[462], despite the fact that the underlayingcryptographic hash function^{[94][95][96][97]} (Secure Hash Algorithm 1^{[202][203][204]}) is considered insecure^{[205][206][207][208][209][210][211]}.

If your application or requirements specifically call for the use of a message authentication code^{[135][136][137][138]} that does not provide authenticated encryption^[74] prefer block cipher mode of operation^{[82][83][84][85][86]} (eg: counter with CBC-MAC^[32][33][34], Galois/Counter Mode^{[46][47][48][49]} or message authentication code^{[135][136][137][138]} (eg: Poly1305^[458][459]) that proved authenticated encryption over the ones which does not provide it. In case of a hashed message authentication code^{[139][140][141][142][143][144][145]} prefer message authentication code^{[135][136][137][138]} based on Secure Hash Algorithm 2^{[212][213][214]} over the ones based on Secure Hash Algorithm 1^{[202][203][204]}.