[gnutls-devel] GnuTLS | WIP: Support for GOST-CTR ciphersuites from draft-smyshlyaec-tls12-gost-suites (!1144)

Development of GNU's TLS library gnutls-devel at lists.gnutls.org
Sun Dec 29 11:29:31 CET 2019

Dmitry Eremin-Solenikov commented:

@nmav This MR manifests a crypto-api issue.

CTR-ACPKM (CTR with internal rekeying, see [RFC 8645](https://www.rfc-editor.org/rfc/rfc8645.html) modes are defined with an integer parameter called section size. It is the amount of data to be encrypted using a single key before rekeying. This parameter is a part of encryption scheme, but it is not fixed. So e.g. TLS 1.2 will use 1024 bytes for MAGMA-CTR-ACPKM and 4096 bytes for KYZNYECHIK-CTR-ACPKM. However provided test vectors use sections of 256 bits (32 bytes). While this looks like a lesser problem (one can regenerate test vectors big enough to actually test rekeying transformation), this is actually only a partial solution. For example CMS files are going to use 256-KBytes sections.

OpenSSL solved this by adding a "control" to set section size. However GnuTLS lacks such "controls".

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