On Mon, Jun 13, 2022 at 4:34 AM Jochen Bern <Jochen.Bern@xxxxxxxxx> wrote: > On 10.06.22 16:50, Dmitry Belyavskiy wrote: > > > There is a need to increase RSA key requirements to make the > > installations more secure. Just updating the default compiled-in > > value isn't an option because it may significantly break legacy > > systems compatibility. This PR [1] introduces a new configuration > > option MinRSABits to be managed for security's sake. > > > > If this approach is OK for upstream, please let me know and I will > > improve this PR according to the feedback. > > I realize that with the *current* selection of algorithms available > in OpenSSH, fine-grained control of minimum key size almost(!) is an > RSA-only topic, but nonetheless I wonder whether newly-defined > config syntax thereto should be aimed at extensibility to other > cryptalgorithms ... That ship sailed long ago: $ grep SSH_RSA_MINIMUM_MODULUS_SIZE sshkey.h #define SSH_RSA_MINIMUM_MODULUS_SIZE 1024 It’s not worth it to attempt to refactor this approach, as with both the ecdsa family and ed25519, the cipher name specifies the security strength. Dmitry’s merge request both defaults MinRSABits to SSH_RSA_MINIMUM_MODULUS_SIZE, and prohibits setting MinRSABits to anything less than SSH_RSA_MINIMUM_MODULUS_SIZE. So unless the administrator specifically sets MinRSABits to something greater than 1024, it will not change the behavior of OpenSSH. It also documents MinRSABits in the man pages, and includes MinRSABits in “ssh -G” output. All of this seems perfectly reasonable. NIST Special Publication 800-131A (1) prohibits the use of RSA keys with len(n) < 2048 for all uses but legacy digital signature verification, and an increasing number of sites (including ours) must comply with NIST SP 800-131A. Having the MinRSABits option would make our lives easier with respect to compliance. (1) https://doi.org/10.6028/NIST.SP.800-131Ar2 _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
