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ANNOUNCE: Nettle-3.7.2

From: Niels Möller
Subject: ANNOUNCE: Nettle-3.7.2
Date: Sun, 21 Mar 2021 10:24:11 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux)

I've prepared a new bug-fix release of Nettle, a low-level
cryptographics library, to fix a serious bug in the function to verify
ECDSA signatures. Implications include an assertion failure, which could
be used for denial-of-service, when verifying signatures on the
secp_224r1 and secp521_r1 curves. More details in NEWS file below.

Upgrading is strongly recomended.

The Nettle home page can be found at, and the manual at

The release can be downloaded from


NEWS for the Nettle 3.7.2 release

        This is a bugfix release, fixing a bug in ECDSA signature
        verification that could lead to a denial of service attack
        (via an assertion failure) or possibly incorrect results. It
        also fixes a few related problems where scalars are required
        to be canonically reduced modulo the ECC group order, but in
        fact may be slightly larger.

        Upgrading to the new version is strongly recommended.

        Even when no assert is triggered in ecdsa_verify, ECC point
        multiplication may get invalid intermediate values as input,
        and produce incorrect results. It's trivial to construct
        alleged signatures that result in invalid intermediate values.
        It appears difficult to construct an alleged signature that
        makes the function misbehave in such a way that an invalid
        signature is accepted as valid, but such attacks can't be
        ruled out without further analysis.

        Thanks to Guido Vranken for setting up the fuzzer tests that
        uncovered this problem.

        The new version is intended to be fully source and binary
        compatible with Nettle-3.6. The shared library names are and, with sonames and

        Bug fixes:

        * Fixed bug in ecdsa_verify, and added a corresponding test

        * Similar fixes to ecc_gostdsa_verify and gostdsa_vko.

        * Similar fixes to eddsa signatures. The problem is less severe
          for these curves, because (i) the potentially out or range
          value is derived from output of a hash function, making it
          harder for the attacker to to hit the narrow range of
          problematic values, and (ii) the ecc operations are
          inherently more robust, and my current understanding is that
          unless the corresponding assert is hit, the verify
          operation should complete with a correct result.

        * Fix to ecdsa_sign, which with a very low probability could
          return out of range signature values, which would be
          rejected immediately by a verifier.

Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677.
Internet email is subject to wholesale government surveillance.

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