OpenPGP Public-Key Encrypted Session Key Packet Key ID generation

Question

Im probably just not reading something again, but:

RFC 4880 says that a OpenPGP Public-Key Encrypted Session Key Packet (tag 1) is made up of

- A one-octet number giving the version number of the packet type.
The currently defined value for packet version is 3.
- An eight-octet number that gives the Key ID of the public key to
which the session key is encrypted. If the session key is
encrypted to a subkey, then the Key ID of this subkey is used
here instead of the Key ID of the primary key.
- A one-octet number giving the public-key algorithm used.
- A string of octets that is the encrypted session key. This
string takes up the remainder of the packet, and its contents are
dependent on the public-key algorithm used.

i encrypted (using a working pgp program) a string of 0123456789abcdef using a key whose KeyID is 30522545CF77DD86, but the pgp message packet that resulted had a KeyID of F940C4301A67779D in its tag 1 data. it is certainly not the KeyID from the public key i used.

what do i need to do to get that keyid? what am i not seeing?

key used to encrypt data:

-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: BCPG v1.39

mQGiBE5B0h8RBAD533Z5bK1IpBx02QyQL0QoJE4uFRIMGDiwXuwmZzVl+R7Vlurd
GRLsCCbE6vOOh7XQVZGzLEBy9WNzZ9m+EbCfSVAYkjS6FhLws6hG6irrnS+b3JBf
gFJ8vNGF9Z7bhx+7y7NBk0IMyWkGnUkcnav73t5FQUI2faEBN4c/yAGJZwCgjcB7
3akWk9XVWvTCsiMXxpyvkukEALXsvB6cOoFEtQq9cQHjP63fBlvD94dhhMiM0cH6
hW9JotxdK+cxFGG9ZIWgoN2PWbMJka/H4W5EL6tS+YiNAR7I1Ozkt6X16GjnQUzZ
MlSpleK+KiKVN2anRaPEoOIinHrE3ZXd6QlJ/4+OJn4IVWmSEaJpFf4QNgvEu4rh
xinyBAD2RNzREOA+wpnFZ4lDt9NZXmXdxQME/l0J9XcvWhpGsxA/MATQKImy7N49
7GT/M38F+TrpBobag1O3buE99fOLyws4Tbc+sZMdHxoiGZDAIRNQS2rv475E6ktj
7vd5CYvOkA6+8sX1+hPcNlkHtHB1OFkJRsYp6k0zkyC9adjBM7QTYWJjIDxtYWtj
bUBhYWEuY29tPohGBBMRAgAGBQJOQdIfAAoJEDBSJUXPd92GRSQAoItbtbToOg7a
/hcg2sA/aBEQNwuxAKCGR69vmSoCWoBP5waPk0UsjM3BSbjMBE5B0h8QAgCUlP7A
lfO4XuKGVCs4NvyBpd0KA0m0wjndOHRNSIz44x24vLfTO0GrueWjPMqRRLHO8zLJ
S/BXO/BHo6ypjN87Af0VPV1hcq20MEW2iujh3hBwthNwBWhtKdPXOndJGZaB7lsh
LJuWv9z6WyDNXj/SBEiV1gnPm0ELeg8Syhy5pCjMAf9QHehP2eCFqfEwTAnaOlA6
CU+rYHKPZaI9NUwCA7qD2d93/l08/+ZtFvejZW1RWrJ8qfLDRtlPgRzigoF/CXbR
iEYEGBECAAYFAk5B0h8ACgkQMFIlRc933YZRrACfUnWTjHHN+QsEEoJrwRvFmvzj
bR4An24pTpeeN+I6R59O/sdmYsAhjULX
=sStS
-----END PGP PUBLIC KEY BLOCK-----

encrypted data: 0123456789abdef

-----BEGIN PGP MESSAGE-----
Version: BCPG v1.39

hI4D+UDEMBpnd50QAf9bWG97E9FfnSKB/WpVcBtLJqk5f/Ih9YZTUDULDZpSE0TP
ObJnCs91okOv6/BtDRDZ84ChF5pOZezb5+aL3TW5AfwK3gJ7nPTlmZOm5Kf7qOfB
n307xpn0qRw395y1mfOm10TsMpaCkbSvwjhqPi8hRMM17y29OsqGLstZdeAaNTGt
0mwB7EiZti4jOUF3/SCNnn2vA9hVc6o6c0l0h5vQOF0L+eL1Pmhg8RcFT4kHRnI/
A+Ad4hsbOxD1vvzZHx2iETkt1JmNTHmOOY5Cw/n+sFlU9JzZpzAtqwUjjnyN8NjQ
6NbpwL6gebTJCVTNW2c=
=kI32
-----END PGP MESSAGE-----

Answer 1

An OpenPGP "key" is actually a structure that may contain many public keys. Typically, it contains two, a signing key and an encryption key. The signing key is considered the top-level key, as it issues signatures claiming ownership of all the subordinate keys, be they encryption or signing keys.

The key ID of the whole structure as you'd see it in a program is the key ID of the top-level signing key. The keyID if the ESK packet is the key ID of the encryption key. That's why they're different.

Put your whole key into the dump program at http://www.pgpdump.net/ and you'll get the whole thing dumped out for you.