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I'm still confused when reading GnuTLS/Nettle implementation about Camellia-GCM.

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  • $\begingroup$ What is your confusion? The manual states that GNUTLS_CIPHER_CAMELLIA_128_GCM CAMELLIA in GCM mode with 128-bit keys (AEAD). GNUTLS_CIPHER_CAMELLIA_256_GCM CAMELLIA in GCM mode with 256-bit keys (AEAD). $\endgroup$
    – kelalaka
    Apr 10, 2020 at 7:52
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    $\begingroup$ It's probably exactly like AES-GCM but whenever AES would have been invoked instead Camellia is invoked? $\endgroup$
    – SEJPM
    Apr 10, 2020 at 8:35
  • $\begingroup$ @kelalaka no I'm talking about internal implementation. AES-GCM uses AES-CTR to calculate GCM counter hash, but how about Camellia-GCM? shouldn't it use Camellia-CTR to calculate GCM counter hash instead? $\endgroup$
    – Roy
    Apr 10, 2020 at 9:36
  • $\begingroup$ Roy, AES is a primitive and Camellia, too. They have both 128-bit block size and 128,192, and 256-bit key sizes. As @SEJPM noted, you can replace AES with Camellia, and done. $\endgroup$
    – kelalaka
    Apr 10, 2020 at 10:56

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Does Camellia-GCM use Camellia-CTR to create GCM Hash?

GCM is a mode of operation for a 128-bit blocksize block cipher that turns it into an authenticated encryption scheme. It doesn't care about whether you're using AES, Camellia, Twofish, Serpent or MARS. It will work the same way for all of these block ciphers. So yes, Camellia-GCM uses Camellia-CTR internally in exactly the same way AES-GCM uses AES-CTR internally. with Camellia getting the exact same inputs as AES.

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