If Edward Snowden does have a pgp key (I can't find one online), it hasn't been revealed in this message. It looks like the signing and encryption keys are the same:
gpg: armor: BEGIN PGP MESSAGE
gpg: armor header: Version: GnuPG/MacGPG2 v2.0.19 (Darwin)
gpg: armor header: Comment: GPGTools - http://gpgtools.org
:pubkey enc packet: version 3, algo 1, keyid 5B50940B79DEBE35
data: [4096 bits]
gpg: public key is 79DEBE35
:encrypted data packet:
length: unknown
mdc_method: 2
gpg: encrypted with RSA key, ID 79DEBE35
gpg: decryption failed: secret key not available
Of course, they could have used --hidden-encrypt-to, but I think it's more likely a publicity stunt.
Oh, and if you do find a key claiming to be for Edward Snowden online, verify that it's actually him, ideally through the web of trust, and that it isn't just a key that was created after the news was leaked. I'd be wary of any keys on keyservers claiming to be him that have been uploaded after he went public with this.
If --hidden-encrypt-to is used, there still will be signs of that. Specifically, the message addressed to 0x0000000 and the recipient will basically brute force it uses every key he/she has.
Having said, that, according to PGP Dump
Old: Public-Key Encrypted Session Key Packet(tag 1)(524 bytes)
New version(3)
Key ID - 0x5B50940B79DEBE35
Pub alg - RSA Encrypt or Sign(pub 1)
RSA m^e mod n(4096 bits) - ...
-> m = sym alg(1 byte) + checksum(2 bytes) +
PKCS-1 block type 02
New: Symmetrically Encrypted and MDC Packet(tag 18)(4096
bytes) partial start
Ver 1
Encrypted data [sym alg is specified in pub-key
encrypted session key]
(plain text + MDC SHA1(20 bytes))
New: (1024 bytes) partial continue
New: (18 bytes) partial end
It looks like we can merely see that the message is destined to 0x5B50940B79DEBE35. We won't be able to tell who's signer until it is decrypted.
Oh, and if you do find a key claiming to be for Edward Snowden online, verify that it's actually him, ideally through the web of trust, and that it isn't just a key that was created after the news was leaked. I'd be wary of any keys on keyservers claiming to be him that have been uploaded after he went public with this.