#!/bin/sh
# mverify MSG - verify a OpenPGP or SMIME message

# Needs gpg2 (for OpenPGP) and openssl (for SMIME).

if command -v gpg2 >/dev/null; then
	GPG=gpg2
else
	GPG=gpg
fi

[ "$#" -eq 0 ] && set -- .

mshow -t "$1" | DOS2UNIX='/
$/!s/$/
/' awk -v "msg=$1" '
{ match($0, "^ *"); indent = RLENGTH }
$2 == "text/plain" { plain++ }
$2 == "multipart/signed" { signed = 0+$1; si = indent; next }
signed && !content && indent == si+2 { content = 0+$1; next }
signed && content && !signature && indent == si+2 { signature = 0+$1; type = $2 }
function q(a) { gsub("\\47", "\47\\\47\47", a); return "\47"a"\47" }
END {
	if (type == "" && plain) {  // guess plain text armored signature
		exit(system("mshow -r " q(msg) " | '$GPG' --verify"));
	} else if (type == "") {
		print("No signature found.")
		exit(100)
	} else if (type == "application/pgp-signature") {
		exit(system("mshow -r -O " q(msg) " " q(content) \
			" | sed $DOS2UNIX | " \
			" { mshow -O " q(msg) " " q(signature) \
			" | '$GPG' --verify - /dev/fd/3; } 3<&0"))
	} else if (type == "application/pkcs7-signature") {
		exit(system("mshow -r -O " q(msg) " " q(signed) \
			" | openssl smime -verify"))
	} else {
		print("Cannot verify signatures of type " type ".")
		exit(2)
	}
}
'