Re: Avoid recipient-compatibility SHA1

2020-11-19 Thread Stefan Claas via Gnupg-users
Hi Neal, thanks a lot for the detailed explanation! Best regards Stefan On Thu, Nov 19, 2020 at 7:52 AM Neal H. Walfield wrote: > > Hi Stefan, > > A chosen-prefix collision attack works as follows: an attacker chooses > two message prefixes, and then uses near collisions blocks (in the > SHA-1

Re: Avoid recipient-compatibility SHA1

2020-11-18 Thread Neal H. Walfield
Hi Stefan, A chosen-prefix collision attack works as follows: an attacker chooses two message prefixes, and then uses near collisions blocks (in the SHA-1 is a Shambles paper they needed about 10 such 512-bit blocks) to align the internal state of the two hashes. Since SHA-1 is a streaming

Re: Avoid recipient-compatibility SHA1

2020-11-18 Thread Phil Pennock via Gnupg-users
On 2020-11-17 at 22:18 -0700, Mark wrote: > Not to ask a stupid question but how can you tell which algorithm your > keys are using and if using SHA1 update them to a more secure one? I have a better answer than my previous one, because the very next mailing-list I read has a post today from the

Re: Avoid recipient-compatibility SHA1

2020-11-18 Thread Phil Pennock via Gnupg-users
On 2020-11-17 at 22:18 -0700, Mark wrote: > Not to ask a stupid question but how can you tell which algorithm your > keys are using and if using SHA1 update them to a more secure one? With GnuPG, `gpg --list-packets` shows a lot of fine detail, but unless you're familiar with the standards it can

Re: Avoid recipient-compatibility SHA1

2020-11-18 Thread Ernst G Giessmann via Gnupg-users
Am 2020-11-18 um 14:30 schrieb Stefan Claas: On Tue, Nov 17, 2020 at 11:11 PM Ernst G Giessmann via Gnupg-users wrote: The answer to the second question is: A SHA-1 collision of two documents D1 and D2 means that the hash values Hash(D1) and Hash(D2) are equal, which in turn means that

Re: Avoid recipient-compatibility SHA1

2020-11-18 Thread Stefan Claas via Gnupg-users
On Wed, Nov 18, 2020 at 2:30 PM Stefan Claas wrote: > > On Tue, Nov 17, 2020 at 11:11 PM Ernst G Giessmann via Gnupg-users > wrote: > > > > The answer to the second question is: > > > > A SHA-1 collision of two documents D1 and D2 means that the hash values > > Hash(D1) and Hash(D2) are equal,

Re: Avoid recipient-compatibility SHA1

2020-11-18 Thread Stefan Claas via Gnupg-users
On Tue, Nov 17, 2020 at 11:11 PM Ernst G Giessmann via Gnupg-users wrote: > > The answer to the second question is: > > A SHA-1 collision of two documents D1 and D2 means that the hash values > Hash(D1) and Hash(D2) are equal, which in turn means that (regardless > who signs) any signature of D1

Re: Avoid recipient-compatibility SHA1

2020-11-18 Thread Stefan Claas via Gnupg-users
Thank you for your reply, much appreciated! I will however ask also Ernst here again the same question one more time again, as an illustrative example. Regards Stefan On Mon, Nov 2, 2020 at 3:25 PM Phil Pennock via Gnupg-users wrote: > > On 2020-11-02 at 13:49 +0100, Werner Koch via Gnupg-users

Re: Avoid recipient-compatibility SHA1

2020-11-17 Thread Mark
Not to ask a stupid question but how can you tell which algorithm your keys are using and if using SHA1 update them to a more secure one? Thanks, On 11/17/2020 4:13 PM, Phil Pennock via Gnupg-users wrote: The current state of SHA1 is "dangerously exposed, you should be hurrying for the exits,

Re: Avoid recipient-compatibility SHA1

2020-11-17 Thread Phil Pennock via Gnupg-users
On 2020-11-17 at 15:47 +, Stefan Claas wrote: >} Since 2005, SHA-1 has not been considered secure against well-funded >} opponents;[4] as of 2010 many organizations have recommended its >} replacement.[5][6][7] NIST formally deprecated use of SHA-1 in 2011 >} and disallowed its use for digital

Re: Avoid recipient-compatibility SHA1

2020-11-17 Thread Ernst G Giessmann via Gnupg-users
The answer to the second question is: A SHA-1 collision of two documents D1 and D2 means that the hash values Hash(D1) and Hash(D2) are equal, which in turn means that (regardless who signs) any signature of D1 (be it OpenPGP or SMIME) can also be used as a signature of D2. Any signer and any

Re: Avoid recipient-compatibility SHA1

2020-11-17 Thread Stefan Claas via Gnupg-users
On Mon, Nov 2, 2020 at 2:25 PM Phil Pennock via Gnupg-users wrote: > > On 2020-11-02 at 13:49 +0100, Werner Koch via Gnupg-users wrote: > > On Fri, 30 Oct 2020 00:10, Phil Pennock said: > > > recipient. That's fine. I'd rather create pressure for people to fix > > > their systems to use modern

Re: Avoid recipient-compatibility SHA1

2020-11-02 Thread Phil Pennock via Gnupg-users
On 2020-11-02 at 13:49 +0100, Werner Koch via Gnupg-users wrote: > On Fri, 30 Oct 2020 00:10, Phil Pennock said: > > recipient. That's fine. I'd rather create pressure for people to fix > > their systems to use modern cryptography than cater to their brokenness > > with sensitive messages. > >

Re: Avoid recipient-compatibility SHA1

2020-11-02 Thread Werner Koch via Gnupg-users
On Fri, 30 Oct 2020 00:10, Phil Pennock said: > I just sent a message to N recipients, and I think one of them probably > has some preference algorithm in their key details, because this one > mail was signed using SHA1, not my defaults. Fixed: commit 15746d60d492f5792e4a179ab0a08801b4049695

Avoid recipient-compatibility SHA1

2020-10-29 Thread Phil Pennock via Gnupg-users
Folks, Normally everything I do with GnuPG is using SHA256 digests, and I normally keep "weak-digest SHA1" in my gpg.conf file. I just sent a message to N recipients, and I think one of them probably has some preference algorithm in their key details, because this one mail was signed using SHA1,