.\" $OpenBSD: ASN1_item_digest.3,v 1.1 2021/11/07 15:29:01 schwarze Exp $
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.\" Copyright (c) 2021 Ingo Schwarze <schwarze@openbsd.org>
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.Dd $Mdocdate: November 7 2021 $
.Dt ASN1_ITEM_DIGEST 3
.Os
.Sh NAME
.Nm ASN1_item_digest
.Nd DER-encode and hash an ASN.1 value
.Sh SYNOPSIS
.In openssl/x509.h
.Ft int
.Fo ASN1_item_digest
.Fa "const ASN1_ITEM *it"
.Fa "const EVP_MD *type"
.Fa "void *val_in"
.Fa "unsigned char *md"
.Fa "unsigned int *s"
.Fc
.Sh DESCRIPTION
.Fn ASN1_item_digest
assumes that that
.Fa val_in
is an
.Vt ASN1_VALUE
of the type specified by
.Fa it ,
encodes it into DER format by calling
.Xr ASN1_item_i2d 3 ,
hashes the resulting byte array using the digest
.Fa type
by calling
.Xr EVP_Digest 3 ,
places the digest value into
.Pf * Fa md ,
and, unless
.Fa s
is
.Dv NULL ,
places the length in bytes of the digest into
.Pf * Fa s .
Providing a buffer
.Pf * Fa md
large enough to contain the digest is the responsibility of the caller;
providing a buffer of
.Dv EVP_MAX_MD_SIZE
bytes is recommended.
.Sh RETURN VALUES
.Fn ASN1_item_digest
returns 1 for success or 0 if encoding or hashing fails.
.Sh SEE ALSO
.Xr ASN1_item_i2d 3 ,
.Xr ASN1_item_sign 3 ,
.Xr EVP_Digest 3
.Sh HISTORY
.Fn ASN1_item_digest
first appeared in OpenSSL 0.9.7 and has been available since
.Ox 3.1 .