Knowledge Base

DH (Fixed Diffie-Hellman Ephemeral)

Static Diffie-Hellman^[429][430] is a variant of Diffie-Hellman^{[99][100][101][102][103]} key exchange^[133] protocol 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.

Remove the cipher suite from the list of cipher suites supported by your server or replace the cipher suite with it's Ephemeral Diffie-Hellman^{[405][406][407][408]} version.

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]}.

AES-256

Encryption algorithm Advanced Encryption Standard^{[302][303][304][305][306][307][308][309]} is a block cipher^{[78][79][80][81]} for which there is no known practical attack that would allow the attacker to recover the encrypted text without knowledge of the key when the algorithm is implemented correctly. However improper implementations may lead to a side-channel attack^[69][70][71] as it has happened in case of OpenSSL^{[395][396] [310][311][312]}.

Prefer cipher suites with greater key size of AES (eg: perfer AES-256 over AES-128).

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.

256

The symmetric key^{[185][186][187]} withkey size^[184] more than 128 bits as it is should be according to National Institute of Standards and Technology^[470][471] so it is not vulnerable to preimage attack^[67] and it cannreliably prove that message came from the stated sender (its authenticity) and has not been changed, so connection is not open for a man-in-the-middle attack^[61].

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

128

The block cipher^{[78][79][80][81]} uses a block size^[87] larger than 64 bits, so it is not vulnerable to sweet32 attack^{[22][23][24][25]}.

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]}.