[dev-crypto-csharp] Exctract PgpPublicKey object from signed public key.

[Alexander Voronin]

Hi! Unfortunately wiki is down and I did not found anything related in
internet. I have following issue.
I have GnuPG signed public key that contains signed public key:

root@ubuntu:~# gpg --import < pkey.asc
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key 771E0A0E: public key "User (User) <u...@domain.com>" imported
gpg: Total number processed: 1
gpg:               imported: 1
root@ubuntu:~#


root@ubuntu:~# gpg --encrypt -r User
gpg: 91A942AE: There is no assurance this key belongs to the named user

pub  4096g/91A942AE 2010-10-29 User (User) <u...@domain.com>
 Primary key fingerprint: BB08 D13A 1AEB 2F23 1767  D912 CCD0 17AF 771E 0A0E
      Subkey fingerprint: E87A 27D3 A3D8 6489 70D8  2D19 2C65 0745 91A9 42AE
....

And so on. So key is correct and usable. To extract PgpPublicKey object
from key I'm using following method:

public static PgpPublicKey PublicKeyFromString(string keyString) {
using (Stream mStream = new MemoryStream(StringToBytes(keyString))) {
 using (Stream inputStream = PgpUtilities.GetDecoderStream(mStream)) {
PgpPublicKeyRingBundle pgpPub = new PgpPublicKeyRingBundle(inputStream);
 foreach (PgpPublicKeyRing kRing in pgpPub.GetKeyRings()) {
foreach (PgpPublicKey pKey in kRing.GetPublicKeys()) {
 if (pKey.IsEncryptionKey) {
return pKey;
 }
}
 }
}
 }
// not found
 throw new ArgumentException(SJ.Resources.ErrorPGPNoKeysInKeyRing);
}

The problem I see - kRing.GetPublicKeys() returns two elements - one of
them public key itself and second one is key sign. But public key returned
with attribute IsEncryptionKey set to false, and sign returned with
IsEncryptionKey set to true. I can't use this PgpPublicKey object for
encryption, and of course can't use sign for this puprose.
kRing.GetPublicKey() also returns public key with IsEncryptionKey  set to
false.

When I got public key using this method it looks usable (untill I'm trying
to encrypt anything) and I can even save them in armored format. But after
this GnuPG import says:

root@ubuntu:~# gpg --import < pkey-extracted.asc
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key 771E0A0E: public key "User (User) <u...@domain.com>" imported
gpg: Total number processed: 1
gpg:               imported: 1
root@ubuntu:~# gpg --encrypt -r User
gpg: Darkterror: skipped: unusable public key
gpg: [stdin]: encryption failed: unusable public key
root@ubuntu:~#

Is is bug or I missunderstood something? What is correct way to extract
signed public key form keyring?
Thanks in advance!

-- 
когда я опустился на самое дно, снизу мне постучали..