[pacman-dev] [PATCH 3/8] Add function to extract key id from signatures

[Dave Reisner]

On Sat, Nov 03, 2012 at 01:28:17AM +1000, Allan McRae wrote:
> This does not support all possibilities of RFC4880, but it does
> cover every key currently used in Arch Linux.

Hmmm, this function doesn't seem to distinguish between "not a key" and
"not a supported key". Can we return more useful error codes, like
-ENOSYS for unsupported, -EINVAL for not-a-signature packet...

> Signed-off-by: Allan McRae <allan at archlinux.org>
> ---
>  lib/libalpm/signing.c | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  lib/libalpm/signing.h |   2 +
>  2 files changed, 102 insertions(+)
> 
> diff --git a/lib/libalpm/signing.c b/lib/libalpm/signing.c
> index 9d56aba..6b13522 100644
> --- a/lib/libalpm/signing.c
> +++ b/lib/libalpm/signing.c
> @@ -948,4 +948,104 @@ int SYMEXPORT alpm_siglist_cleanup(alpm_siglist_t *siglist)
>  	return 0;
>  }
>  
> +/**
> + * Extract the Issuer Key ID from a signature
> + * @param sig PGP signature
> + * @param len length of signature
> + * @param keys a pointer to storage for key IDs
> + * @return 0 on success, -1 on error
> + */
> +int _alpm_extract_keyid(const unsigned char *sig, size_t len, alpm_list_t **keys)
> +{
> +	size_t pos, spos, blen, hlen, ulen, slen;
> +	pos = 0;
> +
> +	while(pos < len) {
> +		if(!(sig[pos] & 0x80)) {
> +			return -1;
> +		}
> +
> +		if(sig[pos] & 0x40) {
> +			// "new" packet format is not supported
> +			return -1;
> +		}
> +
> +		if(((sig[pos] & 0x3f) >> 2) != 2) {
> +			// signature is not a "Signature Packet"
> +			return -1;
> +		}
> +
> +		switch (sig[pos] & 0x03) {

style nit: switch(foo)

> +			case 0:
> +				blen = sig[pos + 1];
> +				pos = pos + 2;
> +				break;
> +
> +			case 1:
> +				blen = (sig[pos + 1] << 8) | sig[pos + 2];
> +				pos = pos + 3;
> +				break;
> +
> +			case 2:
> +				blen = (sig[pos + 1] << 24) | (sig[pos + 2] << 16) | (sig[pos + 3] << 8) | sig[pos + 4];
> +				pos = pos + 5;
> +				break;
> +
> +			case 3:
> +				// partial body length not supported
> +				return -1;
> +		}
> +
> +		if(sig[pos] != 4) {
> +			// only support version 4 signature packet format
> +			return -1;
> +		}
> +
> +		if(sig[pos + 1] != 0x00) {
> +			// not a signature of a binary document
> +			return -1;
> +		}
> +
> +		pos = pos + 4;
> +
> +		hlen = (sig[pos] << 8) | sig[pos + 1];
> +		pos = pos + hlen + 2;
> +
> +		ulen = (sig[pos] << 8) | sig[pos + 1];
> +		pos = pos + 2;
> +
> +		spos = pos;
> +
> +		while(spos < pos + ulen) {
> +			if(sig[spos] < 192) {
> +				slen = sig[spos];
> +				spos = spos + 1;
> +			} else if(sig[spos] < 255) {
> +				slen = (sig[spos] << 8) | sig[spos + 1];
> +				spos = spos + 2;
> +			} else {
> +				slen = (sig[spos + 1] << 24) | (sig[spos + 2] << 16) | (sig[spos + 3] << 8) | sig[spos + 4];
> +				spos = spos + 5;
> +			}
> +
> +			if(sig[spos] == 16) {
> +				// issuer key ID
> +				char key[16];
> +				size_t i;
> +				for (i = 0; i < 8; i++) {
> +					sprintf(&key[i * 2], "%02hhX", sig[spos + i + 1]);
> +				}
> +				*keys = alpm_list_add(*keys, strdup(key));

Would be nice to be robust against strdup() memory allocation failures here.

> +				break;
> +			}
> +
> +			spos = spos + slen;
> +		}
> +
> +		pos = pos + (blen - hlen - 8);
> +	}
> +
> +	return 0;
> +}
> +
>  /* vim: set ts=2 sw=2 noet: */
> diff --git a/lib/libalpm/signing.h b/lib/libalpm/signing.h
> index a78e4b7..6537ee3 100644
> --- a/lib/libalpm/signing.h
> +++ b/lib/libalpm/signing.h
> @@ -34,6 +34,8 @@ int _alpm_process_siglist(alpm_handle_t *handle, const char *identifier,
>  int _alpm_key_in_keychain(alpm_handle_t *handle, const char *fpr);
>  int _alpm_key_import(alpm_handle_t *handle, const char *fpr);
>  
> +int _alpm_extract_keyid(const unsigned char *sig, size_t len, alpm_list_t **keys);
> +
>  #endif /* _ALPM_SIGNING_H */
>  
>  /* vim: set ts=2 sw=2 noet: */
> -- 
> 1.8.0
> 
>