3

I have a PGP signature:

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2

iQEcBAABCAAGBQJX192XAAoJEBMxnLaYuadNVV8H/j5P9CJUnRfBGEtAXAJry35x
SXgVhx4WsC3uHZmWLaGDtzYg3sfZKgKrYLfJn7NP6vAe3PvxxIVbXw28trAneYlE
bv1ogqBO/waWecJIR+WimeTbHyKK/cEKQk+6nV8Q7/BhxE7RcbeEhbSn+JWhtjwu
UubjKr6KZvSPPD7LeA59E96fSksVypg/Em1ZMM3MzmRHKc6pKJuG2SKLUaN0hPt4
sux6ZKq+yKBz/k/iYkfbazyYK4PZgcRijb9P7Cfkoe5DD2kdMNOFgW3N9+4Zie+O
aQe23xwh5p3rb2/zHTbUU6YcTyAK8Js/xnR4Aih0Nd43tEvOOTXc1NnVe7jE4jE=
=lMwp
-----END PGP SIGNATURE-----

I can use bouncy castle to generate the first couple of lines but there is a =lMwp at the end of the signature that I don't know where to find or what it is.

Is it a checksum of some kind?

3

Is it a checksum of some kind?

Exactly. From RFC 4880 (OpenPGP) Section 6:

  1. Radix-64 Conversions
    ... OpenPGP's Radix-64 encoding is composed of two parts: a base64 encoding of the binary data and a checksum. The base64 encoding is identical to the MIME base64 content-transfer-encoding [RFC2045].
    The checksum is a 24-bit Cyclic Redundancy Check (CRC) converted to four characters of radix-64 encoding by the same MIME base64 transformation, preceded by an equal sign (=) ...
    The checksum with its leading equal sign MAY appear on the first line after the base64 encoded data.

If you want to know how exactly the checksum is computed so you can recreate or verify it just read on in this section.

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