Re: Difference between clearsign and detached signatures?
On Sun, 31 Aug 2014 18:03, gn...@iam.tj said: to see how to do is set the keyring file to use. There doesn't appear to be any function that provides for setting an existing key ring; the best I could find is gpgme_op_import_keys() which talks about: The keyring is an internal propery of GnuPG and thus we can't provide an API in GPGME. What we do instead is to allow swicthing GnuPG's home directory via gpgme_set_engine_info. In my scenario I simply need to tell the crypto engine to use the /etc/apt/trusted.gpg Do you want to use gpgme as a API for gpgv ? It might be useful to consider a new gpgme_protocol for verifying keys using a redefined set of keys. Salam-Shalom, Werner -- Die Gedanken sind frei. Ausnahmen regelt ein Bundesgesetz. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Difference between clearsign and detached signatures?
On 31/08/14 01:47, Ingo Klöcker wrote: On Saturday 30 August 2014 23:11:17 TJ wrote: On 30/08/14 22:20, Ingo Klöcker wrote: I strongly suggest that you have a look at using some Python binding for gpgme instead of messing around with gpg. gpgme is _the_ library for using GnuPG in other programs. Thanks - somehow I'd missed gpgme and the python-gpgme package which is available for Debian/Ubuntu. pygpgme looks to be a very basic wrapper around gpgme but has no documentation about how it deals with type differences. Looking at the API documentation for gpgme the one thing I've not been able to see how to do is set the keyring file to use. There doesn't appear to be any function that provides for setting an existing key ring; the best I could find is gpgme_op_import_keys() which talks about: the general interface to move a key from one crypto engine to another as long as they are compatible. In particular it is used to actually import and make keys permanent which have been retrieved from an external source In my scenario I simply need to tell the crypto engine to use the /etc/apt/trusted.gpg keyring which is what I'm doing with the python-gnupg library currently. I had expected gpgme_set_engine_info() would be the most likely function for setting the key ring. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Difference between clearsign and detached signatures?
I've finally pinned down the issue. The manipulation of the plaintext by clearsign results in the message digest being calculated on different plaintext, as per RFC4880 7.1 Dash-Escaped Text: As with binary signatures on text documents, a cleartext signature is calculated on the text using canonical CRLF line endings. The line ending (i.e., the CRLF) before the '-BEGIN PGP SIGNATURE-' line that terminates the signed text is not considered part of the signed text. The issue stems from the different ways that DOS/Windows and *nix handle line-endings. In DOS/Windows CRLF is the line separator whereas in *nix it is the line terminator. DOS/Windows doesn't require a line-separator at the end of the last line of a text file, whereas *nix requires a line terimantor. I used 3 plaintext test-cases to isolate the issue: Release: A Debian APT archive Release file (all lines end with LF including the last line) Release.CRLF : 'Release' with all line endings converted to CRLF Release.CRLF.2 : 'Release.CRLF' with the final CRLF removed gpg --debug-all --detach-sign --armor ... does not modify the plaintext before generated the message digest (see dbgmd-1.sign). gpg --debug-all --clearsign ... Release.CRLF.2 does *not* modify the plaintext (see dbgmd-1-clearsign). gpg --debug-all --clearsign ... Release.CRLF modifies the plaintext by removing the final CRLF pair (see dbgmd-1-clearsign). gpg --debug-all --clearsign ... Release modifies the plaintext, replacing all LF with CRLF and removing the last lines terminator (see dbgmd-1-clearsign). So to use a detached signature to verify using clearsign format the plaintext must be pre-formatted to be identical to the clearsign generated plaintext form: gpg --debug-all --digest-algo SHA512 --detach-sign --armor --local-user 3591FB89 --output Release.gpg (sed 's/$/\r/' Release | head -c -2) gpg --verify (echo -e -BEGIN PGP SIGNED MESSAGE-\nHash: SHA512\n\n$(sed 's/$/\r/' Release | head -c -2)\n$(cat Release.gpg)) # gpg: Signature made Sat 30 Aug 2014 18:41:52 BST using RSA key ID 3591FB89 # gpg: Good signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org gpg --verify (echo -e -BEGIN PGP SIGNED MESSAGE-\nHash: SHA512\n\n$(cat Release)\n$(cat Release.gpg)) # gpg: Signature made Sat 30 Aug 2014 18:41:52 BST using RSA key ID 3591FB89 # gpg: Good signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org Unfortunately, for plaintext that hasn't been pre-formatted, it means gpg needs modifying in order for it to correctly verify clearsign input that embeds a detached signature rather than a clearsign signature. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Difference between clearsign and detached signatures?
On Thursday 28 August 2014 22:53:52 TJ wrote: I've recently been digging deep into the source-code trying to understand what the differences are between --clearsign and --detach-sign signatures. This came about whilst writing code that calls on gpg --verify on detached signatures; specifically Debian APT archives that contain Release (plaintext) and Release.gpg (detached signature). The aim/hope was to combine the plaintext and detached signature into the armored clearsign format and thus avoid needing to write one of them to the file-system (the other can be supplied via stdin). You can probably use another approach than trying to create a clearsigned text from a signed text and its detached signature. On the command line one can provide both, the detached signature and the signed text, one after the other via stdin by running gpg --verify - - You need to separate the detached signature and the signed stuff with an EOT, e.g. on the console first you enter the armored detached signature and terminate it with Ctrl+D, then you enter the signed text and terminate it with Ctrl+D. BTW, which language do you want to write the code in? Regards, Ingo signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Difference between clearsign and detached signatures?
On 30/08/14 22:20, Ingo Klöcker wrote: On Thursday 28 August 2014 22:53:52 TJ wrote: The aim/hope was to combine the plaintext and detached signature into the armored clearsign format and thus avoid needing to write one of them to the file-system (the other can be supplied via stdin). You can probably use another approach than trying to create a clearsigned text from a signed text and its detached signature. On the command line one can provide both, the detached signature and the signed text, one after the other via stdin by running gpg --verify - - You need to separate the detached signature and the signed stuff with an EOT, e.g. on the console first you enter the armored detached signature and terminate it with Ctrl+D, then you enter the signed text and terminate it with Ctrl+D. This would solve the issue I'm dealing with, but I can't get it to work here: gpg --verify - - (echo -ne $(cat Release.gpg)\004$(cat Release)\004) gpg: Signature made Sat 30 Aug 2014 22:58:07 BST using RSA key ID 3591FB89 gpg: BAD signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org cat -e (echo -ne $(cat Release.gpg)\004$(cat Release)\004) | grep END # -END PGP SIGNATURE-^DOrigin: Ubuntu$ With --debug-all I noticed that dgbmd-1.verify is empty, which indicates no plaintext was received. BTW, which language do you want to write the code in? Well, I'm working in C to add another option to gpg, but the code that needs this is a Python library (that imports python-gnupg) that enables the regular verification of the GPG signatures of APT archive 'Release' files in all Debian/Ubuntu/related-distro mirrors world-wide. If I can find a way to pass both plaintext and detached signature via stdin that would solve the issue - I'm trying to avoid any need to create temporary files on the file-system. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Difference between clearsign and detached signatures?
On Saturday 30 August 2014 23:11:17 TJ wrote: On 30/08/14 22:20, Ingo Klöcker wrote: BTW, which language do you want to write the code in? Well, I'm working in C to add another option to gpg, but the code that needs this is a Python library (that imports python-gnupg) that enables the regular verification of the GPG signatures of APT archive 'Release' files in all Debian/Ubuntu/related-distro mirrors world-wide. I strongly suggest that you have a look at using some Python binding for gpgme instead of messing around with gpg. gpgme is _the_ library for using GnuPG in other programs. The following message from last year lists two Python bindings: http://lists.gnupg.org/pipermail/gnupg-users/2013-April/046477.html Regards, Ingo signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Difference between clearsign and detached signatures?
On Thursday 28 August 2014 22:53:52 TJ wrote: I've recently been digging deep into the source-code trying to understand what the differences are between --clearsign and --detach-sign signatures. The RFC is probably much easier to read than the source code: http://tools.ietf.org/html/rfc4880 This came about whilst writing code that calls on gpg --verify on detached signatures; specifically Debian APT archives that contain Release (plaintext) and Release.gpg (detached signature). The aim/hope was to combine the plaintext and detached signature into the armored clearsign format and thus avoid needing to write one of them to the file-system (the other can be supplied via stdin). I had thought that the message digest hash (in this case SHA512) should be the same since the input data is the same which-ever signing method is used. This didn't work as I had expected so I have been digging into the source-code to figure out what is different between the two signing methods. In general the message digest hashes will differ. The reason for this is a different canonicalization of the signed text (provided the detached signature is a text document signature; if it's a binary document signature no canonicalization is applied). A main difference is the stripping of trailing whitespace in the text (which is done for cleartext signatures but not for text document signature). For details see http://tools.ietf.org/html/rfc4880#section-5.2.4 and http://tools.ietf.org/html/rfc4880#section-7 Regards, Ingo signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Difference between clearsign and detached signatures?
On 29/08/14 19:03, Ingo Klöcker wrote: On Thursday 28 August 2014 22:53:52 TJ wrote: I've recently been digging deep into the source-code trying to understand what the differences are between --clearsign and --detach-sign signatures. The RFC is probably much easier to read than the source code: http://tools.ietf.org/html/rfc4880 The RFC was fine but, for me, the code is authoritative especially when I suspect implementation differences. I had thought that the message digest hash (in this case SHA512) should be the same since the input data is the same which-ever signing method is used. This didn't work as I had expected so I have been digging into the source-code to figure out what is different between the two signing methods. In general the message digest hashes will differ. The reason for this is a different canonicalization of the signed text (provided the detached signature is a text document signature; if it's a binary document signature no canonicalization is applied). A main difference is the stripping of trailing whitespace in the text (which is done for cleartext signatures but not for text document signature). Yes, I worked on that one too, checking that there was no white-space at end of lines: egrep '[\t ]$' Release | wc -l 0 I also tried replacing LF with CRLF as per 5.2.1. and Signature of a canonical text document. gpg --verify (echo -e -BEGIN PGP SIGNED MESSAGE-\nHash: SHA512\n\n$(sed ':a;N;$!ba;s/\n/\r\n/g' Release)\n$(cat Release.asc.gpg)) # gpg: Signature made Thu 28 Aug 2014 18:32:06 BST using RSA key ID 3591FB89 # gpg: Good signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org gpg --verify (echo -e -BEGIN PGP SIGNED MESSAGE-\nHash: SHA512\n\n$(sed ':a;N;$!ba;s/\n/\r\n/g' Release)\n$(cat Release.Test.detached.gpg)) # gpg: Signature made Thu 28 Aug 2014 19:29:37 BST using RSA key ID 3591FB89 # gpg: BAD signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org Looking at the code the signing path is either of: g10/sign.c::sign_file() g10/clearsign_file() For sign_file() text_filter() and md_filter() are added to the input iobuf filter list. For clearsign_file() copy_clearsig_text() is called, which in turn uses len_without_trailing_chars() to copy the line excluding trailing whitespace from plaintext input to clearsign output. For verify_signatures() and verify_files() (via verify_one_file()), armor_filter() is pushed onto the iobuf filter list then proc_signature_packets() is called, which calls do_proc_packets() which, during IOBUFCTRL_UNDERFLOW calls radix64_read() which skips whitespace characters. This being the case I cannot see any opportunity for the plaintext that is the subject of the message digest hashing to be different, which suggests that something else is added to the hashed value when generating a detached signature. gpg --verify Release.asc # gpg: Signature made Thu 28 Aug 2014 18:32:06 BST using RSA key ID 3591FB89 # gpg: Good signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org gpg --verify Release.Test.detached.gpg Release # gpg: Signature made Thu 28 Aug 2014 19:29:37 BST using RSA key ID 3591FB89 # gpg: Good signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org gpg --verify Release.asc.gpg Release # gpg: Signature made Thu 28 Aug 2014 18:32:06 BST using RSA key ID 3591FB89 # gpg: BAD signature from Test Key (gnupg 1.4.16 Ubuntu 14.04 amd64) detac...@signature.org ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
