Knowledge Base

Rivest–Shamir–Adleman (RSA)

RSA^[320][321] key exchange is a key exchange^[467] that has no forward secrecy^{[135][136][137][138]}, 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^{[310][311][312][313][314][315]} and was affected by variety of attack types: chosen-ciphertext attack^[557] (eg: Bleichenbacher's attack^[76][77], ROBOT attack^{[540][541][542][543]}), side-channel attack^{[106][107][108]} (eg: padding oracle attack^{[45][46][47][48]}, like Bleichenbacher's cat^{[337][338][339][340]}).

Always prefer cipher suites with PFS property over the non-PFS ones. Note that performance considerations implies preferring Ephemeral Elliptic-curve Diffie–Hellman^[91][92] over Ephemeral Diffie-Hellman^{[142][143][144][145]}.

Pre-shared Key (PKS)

The pre-shared key^[124] can ensure authenticity^{[201][202][203]} of the communicating parties mutually based on symmetric key^{[193][194][195]}s that are shared in advance among the parties. Combined with a key exchange^[467] that has forward secrecy^{[135][136][137][138]} property algorithm can protect against dictionary attack^[504][505]s by passive eavesdroppers (but not active attackers). Pre-shared keys with low entropy^[380], may caused by a weakness^{[359][360][361]} of random number generator^[1][2][3], can be easily broken in brute-force attack^[555]. 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.

If your application or requirements specifically call for the use of algorithms which are not used by the leading client applications set the cipher suite order explicitly and cipher suites used by the leading client applications be preferred over the ones which do not used by them.

Salsa20

The stream cipher^[78][79] Salsa20^{[111][112][113]} is considered secure ^[210] and gives better performance for mobile devices.

Prefer stream cipher^[78][79] Salsa20^{[111][112][113]} and it's variants (eg: ChaCha20^{[181][182][183][184]}) in case of mobile devices.

256

The symmetric key^{[193][194][195]} withkey size^[438] more than 128 bits as it is should be according to National Institute of Standards and Technology^[428][429] so it is not vulnerable to preimage attack^[215] 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^[414].

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

SHA-1

message authentication code^{[128][129][130][131]} is a hashed message authentication code^{[418][419][420][421][422][423][424]} which is considered secure^[159], despite the fact that the underlayingcryptographic hash function^{[510][511][512][513]} (Secure Hash Algorithm 1^{[204][205][206]}) is considered insecure^{[370][371][372][373][374][375][376]}.

If your application or requirements specifically call for the use of a message authentication code^{[128][129][130][131]} that does not provide authenticated encryption^[563] prefer block cipher mode of operation^{[293][294][295][296][297]} (eg: counter with CBC-MAC^{[266][267][268]}, Galois/Counter Mode^{[65][66][67][68]} or message authentication code^{[128][129][130][131]} (eg: Poly1305^[289][290]) that proved authenticated encryption over the ones which does not provide it. In case of a hashed message authentication code^{[418][419][420][421][422][423][424]} prefer message authentication code^{[128][129][130][131]} based on Secure Hash Algorithm 2^[71][72][73] over the ones based on Secure Hash Algorithm 1^{[204][205][206]}.