Knowledge Base

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Cipher Suite: TLS_­AES_­256_­GCM_­SHA384

Summary

Name:
TLS_AES_256_GCM_SHA384
IANA Name:
TLS_AES_256_GCM_SHA384
Code:
(0x13, 0x02)
OpenSSL Name:
TLS_AES_256_GCM_SHA384
Protocol Versions:
TLS 1.3

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Components

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Encryption Type
Name

AES-256

Security

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].

Recommendations

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

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Encryption Mode
Name

GCM

Security

block cipher mode of operation[82][83][84][85][86] Galois/Counter Mode[46][47][48][49] is considered secure. It provides authenticated encryption[74] which simultaneously assure the confidentiality[91][92][93] and authenticity[75][76][77] of data.

Recommendations

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.

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Encryption Key Size
Name

256

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.

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Encryption Block Size
Name

128

Security

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].