The Finished message is the first one protected with the just negotiated algorithms, keys, and secrets. MaartenBodewes, yes you’re right, I had this wrong in mind at the time I wrote the answer. Consequently, GCM is not well-suited for use with very short tag lengths or very long messages. Probably answered in this question on the security. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of service , privacy policy and cookie policy , and that your continued use of the website is subject to these policies. According to the authors’ statement, GCM is unencumbered by patents.

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The encrypted text then contains the IV, ciphertext, and authentication tag. Email Required, but never shown.

Galois/Counter Mode

Initialization vector Mode of operation Padding. In general, t may be any one of the following five values: By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Ferguson psudo Saarinen independently described how an attacker can perform optimal attacks against GCM authentication, which meet the lower bound on its security.

For certain applications, t may be 64 or 32, but the use of these two tag lengths constrains the length of the input data and the lifetime of gmc key. From Wikipedia, the free encyclopedia. Lecture Notes in Computer Science.


This process is called function stitching, [13] and while in principle it can be applied to any combination of cryptographic algorithms, GCM is especially suitable.

By using this site, you agree to the Terms of Use and Privacy Policy. Pages using RFC magic links. If we read the Google line information about how the cypher the https communication, it reads: Different block cipher modes bcm operation can have significantly different performance and efficiency characteristics, even when used with the same block cipher.

The Finished message is the first gcn protected with the just negotiated algorithms, keys, and secrets. I’ll update the answer and emphasize that AES is the most common choice.

Suite-B Encryption RFC6379 – Suite-B-GCM-128 / Suite-B-GCM-256

Sign up using Email and Password. Although the same hash function may also be used for the signature, I’m pretty sure that the acceptable hash psuedo are communicated differently i. GCM combines the well-known counter mode of encryption with the new Galois mode of authentication.

The key feature is that the Galois field multiplication used for authentication can be easily computed in parallel.

Like all counter modes, this is essentially a stream cipherand so it is essential that a different IV is used for each stream that is encrypted. Once a side has sent its Finished message and received and validated the Finished message from its peer, it may begin to send and receive application data over the connection.


MaartenBodewes, yes you’re right, I had this wrong in mind at the time I wrote the answer. Impressive performance oseudo have been published for GCM on a number of platforms.

See Maarten’s answer for more details. Retrieved 8 February Note that there is a pseuddo in the formulas in the article. MyUserIsThis 1 5. It just looks at the ID. Block ciphers security summary.


These instructions enable fast multiplication over GF 2 psrudoand can be used with any field representation. The authentication strength depends on the pssudo of the authentication tag, as with all symmetric message authentication codes.

The GF 2 field used is defined by the polynomial. Views Read Edit View history. Jun 21 ’15 at I’ll make sure I spell my questions correctly: GCM has been proven secure in the concrete security model.