OpenBSD Journal

Errata SECURITY FIX: January 5, 2017

Contributed by grey on from the LibreSSL fixed many of the bugs, let's patch some more! dept.

Avoid possible side-channel leak of ECDSA private keys when signing.

A source code patch exists which remedies this problem:

for 6.0.

for 5.9

This is related to CVE-2016-7056 "ECDSA P-256 timing attack key recovery (OpenSSL, LibreSSL, BoringSSL)" Additional details can be read here:

Thanks to M:Tier for raising awareness on this patch.

(Comments are closed)

  1. By Chas ( on

    If I never use P-256, and always set either curve = secp384r1 or curve = secp521r1, then I can safely ignore this problem?

    DJB only approves of the 521 curve in any case (and I always use it unless I'm dealing with Google Chrome):

    To be fair I should mention that there's one standard NIST curve using a nice prime, namely 2^521 - 1; but the sheer size of this prime makes it much slower than NIST P-256.

    1. By Chas ( on

      If you append the following output after the cert in your .pem file, you will force most (capable) OpenSSL implementations to use the 521 curve:


      $ openssl ecparam -list_curves
        secp384r1 : NIST/SECG curve over a 384 bit prime field
        secp521r1 : NIST/SECG curve over a 521 bit prime field
        prime256v1: X9.62/SECG curve over a 256 bit prime field
      $ openssl ecparam -name secp521r1
      -----BEGIN EC PARAMETERS-----
      -----END EC PARAMETERS-----

      The curves above come from Oracle(RedHat) Linux 7.3 - supposedly this functionality was added to OpenSSL by Sun, who was very careful to avoid a number of patents in this implementation. I'm assuming that LibreSSL inherits that code.

      You can check the curve that a remote TLS server is using with s_client:


      $ openssl s_client -connect
      Server Temp Key: ECDH, secp521r1, 521 bits

      Unlike Firefox, Google Chrome does not support the 521 curve, and will fall back to rsa+aes without forward secrecy. The ssllabs scanner will show what curves a browser supports.


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