How to backdoor store-and-forward public key crypto?

[24.Aug 17:15:29] — [~] — tom@vm: % src/pcp1 -V backdoor.vault -l Key ID Type Creation Time Owner 0xF93E7016447D28CC primary secret 2016-08-24T14:54:28 The Government <spooks@the.gov> 0x5C77C305F0BF8333 valid public 2016-08-24T15:13:02 Freddy Victim <victim@gmail.foo>

[24.Aug 17:15:43] — [~] — tom@vm: % echo “for bobbys eyes only” | src/pcp1 -V spiedsender.vault -i 0x616BDDA58845987B -e -O encrypted-for-bobby.asc Enter passphrase to decrypt your secret key: Encrypted 242 bytes for: 0x616BDDA58845987B - Bobby <bobby@local>

[24.Aug 17:16:14] — [~] — tom@vm: % src/pcp1 -V backdoor.vault -I encrypted-for-bobby.asc -d Enter passphrase to decrypt your secret key: for bobbys eyes only Decrypted 21 bytes successfully