.\" $NetBSD: libnetpgpverify.3,v 1.6 2014/02/17 07:23:18 agc Exp $
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.\" Copyright (c) 2012 Alistair Crooks <agc@NetBSD.org>
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.Dd February 16, 2014
.Dt LIBNETPGPVERIFY 3
.Os
.Sh NAME
.Nm libnetpgpverify
.Nd library to verify digital signatures
.Sh LIBRARY
.Lb libnetpgpverify
.Sh SYNOPSIS
.In netpgp/verify.h
.Ft int
.Fo pgpv_read_pubring
.Fa "pgpv_t *pgp" "const void *keyring" "ssize_t size"
.Fc
.Ft size_t
.Fo pgpv_verify
.Fa "pgpv_cursor_t *cursor" "pgpv_t *pgp" "const void *ptr" "ssize_t size"
.Fc
.Ft size_t
.Fo pgpv_get_verified
.Fa "pgpv_cursor_t *cursor" "size_t cookie" "char **ret"
.Fc
.Ft size_t
.Fo pgpv_get_entry
.Fa "pgpv_t *pgp" "unsigned ent" "char **ret"
.Fc
.Ft int
.Fo pgpv_close
.Fa "pgpv_t *pgp"
.Fc
.Sh DESCRIPTION
.Nm
is a small library which will verify a digital signature on a text or
binary document.
It has been kept deliberately small and only uses compression libraries
to function.
.Pp
PGP messages, including key rings, are made up of PGP packets, defined
in RFC 4880.
To match a digital signature, the public key of the signer must be
located in a public key ring.
This library has enough functionality to parse a pubkey keyring,
using
.Fn pgpv_read_pubring
to read the public keys of trusted identities,
and to read files or memory which has already been signed.
The
.Fn pgpv_verify
function is used to verify the signature, either on data, or on memory.
To signal to
.Fn pgpv_verify
to read a file and verify it, the
.Dv size
argument should be set to
.Dv -1
whilst a positive size signals that the pointer value should be that
of signed memory.
.Fn pgpv_verify
returns a cookie if the ignature was verified, or 0 if it did not.
This cookie can subsequently be used to retrieve the data which
was verified.
.Pp
If the signature does match, then the file or memory can be considered as being
verified as being unmodified and unchanged, integrally sound.
.Pp
Signatures have validity dates on them, and it is possible for a signature to
have expired when it is being checked.
If for any reason the signature does not match, then the reason for not
verifying the signature will be stored in the
.Dv why
buffer in the
.Dv pgpv_cursor_t
structure.
.Pp
Occasionally, the memory or contents of the file which matched the signature
will be needed, rather than a boolean value of whether it was verified.
To do this, the
.Fn pgpv_get_verified
function is used.
Arguments to
.Fn pgpv_get_verified
are the cookie returned from the verification, and a buffer
allocated for the returned data and its size.
If an error occurs, or the signature is not verified, a zero value is returned
for the size.
.Nm
stores the starts of the data of all verified matches, and so the entry
number argument is the index of the occurrence of verification.
The first match will have an entry number of 0, the second 1, and so on.
.Pp
The
.Fn pgpv_close
function is used to clean up after all matching and verification has taken place.
It frees and de-allocates all resources used in the verification of the signature.
.Pp
The program used for signing may encode into base64 encoding, and it may also
use embedded compression to make the output smaller than it would otherwise be.
This is handled automatically by
.Nm .
.Sh SEE ALSO
.Xr bn 3 ,
.\" .Xr bzlib2 3 ,
.Xr zlib 3
.Sh STANDARDS
.Rs
.%A J. Callas
.%A L. Donnerhacke
.%A H. Finney
.%A D. Shaw
.%A R. Thayer
.%D November 2007
.%R RFC 4880
.%T OpenPGP Message Format
.Re
.Sh HISTORY
The
.Nm
library first appeared in
.Nx 7.0 .
.Sh AUTHORS
.An Alistair Crooks Aq Mt agc@NetBSD.org