PROV: Add the beginning of a DER writing library

This library is meant to be small and quick.  It's based on WPACKET,
which was extended to support DER writing.  The way it's used is a
bit unusual, as it's used to write the structures backward into a
given buffer.  A typical quick call looks like this:

    /*
     * Fill in this structure:
     *
     * something ::= SEQUENCE {
     *     id OBJECT IDENTIFIER,
     *     x [0] INTEGER OPTIONAL,
     *     y [1] BOOLEAN OPTIONAL,
     *     n INTEGER
     * }
     */
    unsigned char buf[nnnn], *p = NULL;
    size_t encoded_len = 0;
    WPACKET pkt;
    int ok;

    ok =   WPACKET_init_der(&pkt, buf, sizeof(buf)
        && DER_w_start_sequence(&pkt, -1)
        && DER_w_bn(&pkt, -1, bn)
        && DER_w_boolean(&pkt, 1, bool)
        && DER_w_precompiled(&pkt, -1, OID, sizeof(OID))
        && DER_w_end_sequence(&pkt, -1)
        && WPACKET_finish(&pkt)
        && WPACKET_get_total_written(&pkt, &encoded_len)
        && (p = WPACKET_get_curr(&pkt)) != NULL;

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11450)

1 files changed, 1 insertions, 1 deletions

diff --git a/crypto/build.info b/crypto/build.info
index baa31ee8e1..864506a18d 100644
--- a/crypto/build.info
+++ b/crypto/build.info
@@ -71,7 +71,7 @@ $UTIL_COMMON=\
         cryptlib.c params.c params_from_text.c bsearch.c ex_data.c o_str.c \
         ctype.c threads_pthread.c threads_win.c threads_none.c initthread.c \
         context.c sparse_array.c asn1_dsa.c packet.c param_build.c $CPUIDASM \
-        param_build_set.c
+        param_build_set.c der_writer.c
 $UTIL_DEFINE=$CPUIDDEF
 
 SOURCE[../libcrypto]=$UTIL_COMMON \