similar to: OpenSSH and RFC 5114

Greetings, Given the weakness with Diffie-Hellman modp groups less than 2048, is it time to bump the suggested 1024 bit minimum value from the RFC 4419 to a more current 2048 value for OpenSSH 7.0? If so, should this be just a compile-time change, or should there be a new client and server runtime option? Thanks, -- Mark

On 09/24/2017 12:21 AM, Mark D. Baushke wrote: > I suggest you upgrade to a more recent edition of the OpenSSH software. > The most recent release is OpenSSH 7.5 and OpenSSH 7.6 will be released > very soon. This problem is in v7.5 and v7.6. See dh.c:436. > OpenSSH 6.6 was first released on October 6, 2014. I brought up v6.6 to give an example that older clients wouldn't be

Hi, You will be aware of https://weakdh.org/ by now, I presume; the take-home seems to be that 1024-bit DH primes might well be too weak. I'm wondering what (if anything!) you propose to do about this issue, and what Debian might do for our users? openssh already prefers ECDH, which must reduce the impact somewhat, although the main Windows client (PuTTY) doesn't support ECDH yet. But

Also, how are default moduli shipped with OpenSSH for use in diffie-hellman-group-exchange-sha1/sha256 chosen? Are they chosen randomly by developers or are they chosen for security properties? If they are random, why not use moduli from RFC 7919 instead, like Mozilla recommends? On Fri, Feb 15, 2019 at 3:48 AM Mark D. Baushke <mdb at juniper.net> wrote: > > Yegor Ievlev <koops1997

I'm not nearly knowledgeable enough in crypto to fully understand your answer, but I will try. I wonder why moduli are not automatically generated the first time sshd is started though. That would make much more sense than shipping a default moduli file but also asking everyone to replace it with their own. On Fri, Feb 15, 2019 at 5:50 AM Mark D. Baushke <mdb at juniper.net> wrote: >

On 25 September 2017 at 02:32, Mark D. Baushke <mdb at juniper.net> wrote: > [+CC Loganaden Velvindron <logan at hackers.mu>] primary author of > the RFC 4419 refresh draft. https://datatracker.ietf.org/doc/draft-lvelvindron-curdle-dh-group-exchange/ ? Tangent: has any consideration been given to increasing the maximum allowed beyond 8192 bits (which is below the current NIST

Hi, my question is related to the kex algorithm diffie-hellman-group-exchange-sha256 and moduli generation. I've seen that through ssh-keygen, I'm able to re-generate my moduli file used by DH but I'm note sure to understand one point in the ssh-keygen manpage : "Screened DH groups may be installed in /etc/ssh/moduli. It is important that this file contains moduli of a range of

On Fri, 2019-02-15 at 15:57 +1100, Darren Tucker wrote: > That was the original intent (and it's mentioned in RFC4419) however > each moduli file we ship (70-80 instances of 6 sizes) takes about 1 > cpu-month to generate on a lowish-power x86-64 machine. Most of it > is > parallelizable, but even then it'd likely take a few hours to > generate > one of each size. I

I don't think there is any point to generate so many moduli. Actually, 3 moduli of sizes 2048, 3072 and 4096 seem like a sane choice. On Fri, Feb 15, 2019 at 7:58 AM Darren Tucker <dtucker at dtucker.net> wrote: > > On Fri, 15 Feb 2019 at 14:22, Yegor Ievlev <koops1997 at gmail.com> wrote: > > I'm not nearly knowledgeable enough in crypto to fully understand your

https://bugzilla.mindrot.org/show_bug.cgi?id=2302 Bug ID: 2302 Summary: ssh (and sshd) should not fall back to deselected KEX algos Product: Portable OpenSSH Version: 6.7p1 Hardware: All OS: All Status: NEW Severity: security Priority: P5 Component: ssh

https://bugzilla.mindrot.org/show_bug.cgi?id=2302 Bug ID: 2302 Summary: ssh (and sshd) should not fall back to deselected KEX algos Product: Portable OpenSSH Version: 6.7p1 Hardware: All OS: All Status: NEW Severity: security Priority: P5 Component: ssh

A few questions regarding the OpenSSH support for the Diffie Hellman key exchange algorithms: (1) Are the diffie-hellman-group-exchange-sha256", "diffie-hellman-group-exchange-sha1" , "diffie-hellman-group14-sha1" "diffie-hellman-group1-sha1" (as defined in RFCs 4253 and RFC 4419) the complete list of key exchange algorithms supported by OpenSSH? (2) Is there a

Hi, I'm interested in requiring a minimum of 3072-bit DH moduli when using the "diffie-hellman-group-exchange-sha256" kex, so I edited my /etc/ssh/moduli file such that only 3071+ moduli are left. However, when clients ask for a max of 2048-bit moduli, they actually get one (!). I poked around and found that a fallback mechanism exists (dh.c:185), which returns back the

Hi, Can anybody briefly explain the significance of the updated moduli file? Is this a critical update? Should all existing installations update their moduli file? Thanks in advance, -- Dan

> Can this be addressed in ssh_config/sshd_config with the KexAlgorithms setting? weakdh.org/sysadmin.html recommends adding: KexAlgorithms curve25519-sha256 at libssh.org But this thread makes it sound as if it's not necessary. Can anyone confirm? Personally I'm on openssh-6.7. - Grant > You will be aware of https://weakdh.org/ by now, I presume; the take-home seems to be

Hello all, I have recently had cause to dig a little into the specifics of how diffie-hellman-group-exchange-sha256 group sizes work. The belief in the wild, perpetuated by multiple sources of logjam mediation papers and also Andras Stribnik's very influential piece "Secure Secure Shell", is that server operators can force the use of a minimum group size by removing moduli

Hello, On Sun, Sep 22, 2024 at 10:15?AM Kurt Fitzner via openssh-unix-dev <openssh-unix-dev at mindrot.org> wrote: > > I would like to advocate for: > > - Change behaviour of the server to allow server operators to set the > minimum modulus group size allowable for a connection using > diffie-hellman-group-exchange-sha256 > Whether this is by having the server refuse

On 09/22/2017 06:55 PM, Tim Broberg wrote: > Do I understand correctly, that you find the security of group 14 unacceptable and yet you left it enabled? In the end, I'm trying to ensure a minimum equivalent of 128-bits of security. Group14 is 2048-bits, which roughly translates to 112-bits. [1] To this end, I disabled the "diffie-hellman-group14-sha1" and

https://bugzilla.mindrot.org/show_bug.cgi?id=2303 Bug ID: 2303 Summary: ssh (and perhaps even sshd) should allow to specify the minimum DH group sizes for DH GEX Product: Portable OpenSSH Version: 6.7p1 Hardware: All OS: All Status: NEW Severity: security Priority: P5

https://bugzilla.mindrot.org/show_bug.cgi?id=2793 Bug ID: 2793 Summary: DH Group Exchange Incorrect Fallback Product: Portable OpenSSH Version: -current Hardware: All OS: All Status: NEW Severity: major Priority: P5 Component: sshd Assignee: unassigned-bugs at mindrot.org