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Components
B
Key Exchange Method
Name
Kerberos V5 (KRB5)
Security
A Kerberos[220][221][222][223][224][225][226] cipher suite[471][472]s provide secure communication where the authentication and the establishment of a master secret will be done using the client's Kerberos credentials while client and server are mutually authenticated. The Kerberos protocol is considered secure, however it's authentication model is vulnerable to brute-force attack[555] against the key distribution center[44] and there are some protocol specific attacks [530][531]. 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.
Recommendations
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.
B
Authentication Method
Name
Kerberos V5 (KRB5)
Security
A Kerberos[220][221][222][223][224][225][226] cipher suite[471][472]s provide secure communication where the authentication and the establishment of a master secret will be done using the client's Kerberos credentials while client and server are mutually authenticated. The Kerberos protocol is considered secure, however it's authentication model is vulnerable to brute-force attack[555] against the key distribution center[44] and there are some protocol specific attacks [530][531]. 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.
Recommendations
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.
F
Encryption Type
Name
DES-40
Security
Encryption algorithm Data Encryption Standard[96][97][98][99][100] is considered obsolete[400][401][402][403][404][405]. It is weakened against brute-force attack[555]. It cannot provide confidentiality[198][199][200], so connection is available or disclosed to unauthorized individuals, entities, or processes.
Recommendations
Remove the cipher suite from the list of cipher suites supported by your server.
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.
D
Encryption Key Size
Name
40
Security
Any symmetric key[193][194][195] with key size[438] less than 128 bits are disallowed by National Institute of Standards and Technology[428][429] as it is vulnerable to preimage attack[215] 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[414].
Recommendations
Remove the cipher suite from the list of cipher suites supported by your server.
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[567]).
