Knowledge Base

F

Cipher Suite: TLS_­KRB5_­WITH_­RC4_­128_­MD5

Summary

Name:
TLS_KRB5_WITH_RC4_128_MD5
IANA Name:
TLS_KRB5_WITH_RC4_128_MD5
Code:
(0x00, 0x24)
OpenSSL Name:
Protocol Versions:
TLS 1.0,TLS 1.1,TLS 1.2

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Components

B
Key Exchange Method
Name
KRB5 (Kerberos V5)
Security
A Kerberos[215][216][217][218][219][220][221] cipher suite[189][190]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[54] against the key distribution center[132] and there are some protocol specific attacks [222][223]. 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
KRB5
Security
A Kerberos[215][216][217][218][219][220][221] cipher suite[189][190]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[54] against the key distribution center[132] and there are some protocol specific attacks [222][223]. 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
RC4-128
Security
Encryption algorithm Rivest Cipher 4[370][371][372][373] is a stream cipher[182][183] that is more malleable[134] than a block cipher[78][79][80][81]. It has multiple vulnerabilities[375][376][377][378][379] (eg: related-key attack[68], distinguishing attack[60], ...), so attacker can apply statistical analysis against it to recover the encrypted text.
Recommendations
Remove the cipher suite from the list of cipher suites supported by your server.
A+
Encryption Key Size
Name
128
Security
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].
Recommendations
Remove the cipher suite from the list of cipher suites supported by your server.
B
Message Authentication Code
Name
MD5
Security
message authentication code[135][136][137][138] is a hashed message authentication code[139][140][141][142][143][144][145] which is considered secure[456][457], despite the fact that the underlaying cryptographic hash function[94][95][96][97] (MD5[197][198][199]) is considered insecure[200][201] as it vulnerable to collision attack[57] in practice and to preimage attack[67] in theory.
Recommendations
Leading client applications do not use this type of message authentication code[135][136][137][138]. 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 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 MD5[197][198][199].