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common: Add functions to help create DER objects.

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* common/tlv.c (put_tlv_to_membuf): New.
(get_tlv_length): New.
* common/tlv.h: Include membuf.h.

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2020-04-23 09:51:15 +02:00
parent 8dfef5197a
commit 5d015b38eb
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
2 changed files with 111 additions and 2 deletions
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101
common/tlv.c
View File

@ -157,6 +157,107 @@ find_tlv_unchecked (const unsigned char *buffer, size_t length,
}
/* Write TAG of CLASS to MEMBUF. CONSTRUCTED is a flag telling
* whether the value is constructed. LENGTH gives the length of the
* value, if it is 0 undefinite length is assumed. LENGTH is ignored
* for the NULL tag. TAG must be less that 0x1f. */
void
put_tlv_to_membuf (membuf_t *membuf, int class, int tag,
int constructed, size_t length)
{
unsigned char buf[20];
int buflen = 0;
int i;
if (tag < 0x1f)
{
*buf = (class << 6) | tag;
if (constructed)
*buf |= 0x20;
buflen++;
}
else
BUG ();
if (!tag && !class)
buf[buflen++] = 0; /* end tag */
else if (tag == TAG_NULL && !class)
buf[buflen++] = 0; /* NULL tag */
else if (!length)
buf[buflen++] = 0x80; /* indefinite length */
else if (length < 128)
buf[buflen++] = length;
else
{
/* If we know the sizeof a size_t we could support larger
* objects - however this is pretty ridiculous */
i = (length <= 0xff ? 1:
length <= 0xffff ? 2:
length <= 0xffffff ? 3: 4);
buf[buflen++] = (0x80 | i);
if (i > 3)
buf[buflen++] = length >> 24;
if (i > 2)
buf[buflen++] = length >> 16;
if (i > 1)
buf[buflen++] = length >> 8;
buf[buflen++] = length;
}
put_membuf (membuf, buf, buflen);
}
/* Return the length of the to be constructed TLV. CONSTRUCTED is a
* flag telling whether the value is constructed. LENGTH gives the
* length of the value, if it is 0 undefinite length is assumed.
* LENGTH is ignored for the NULL tag. TAG must be less that 0x1f. */
size_t
get_tlv_length (int class, int tag, int constructed, size_t length)
{
size_t buflen = 0;
int i;
(void)constructed; /* Not used, but passed for uniformity of such calls. */
if (tag < 0x1f)
{
buflen++;
}
else
{
buflen++; /* assume one and let the actual write function bail out */
}
if (!tag && !class)
buflen++; /* end tag */
else if (tag == TAG_NULL && !class)
buflen++; /* NULL tag */
else if (!length)
buflen++; /* indefinite length */
else if (length < 128)
buflen++;
else
{
i = (length <= 0xff ? 1:
length <= 0xffff ? 2:
length <= 0xffffff ? 3: 4);
buflen++;
if (i > 3)
buflen++;
if (i > 2)
buflen++;
if (i > 1)
buflen++;
buflen++;
}
return buflen + length;
}
/* ASN.1 BER parser: Parse BUFFER of length SIZE and return the tag
and the length part from the TLV triplet. Update BUFFER and SIZE
on success. */

12
common/tlv.h
View File

@ -30,6 +30,7 @@
#ifndef SCD_TLV_H
#define SCD_TLV_H 1
#include "membuf.h"
enum tlv_tag_class {
CLASS_UNIVERSAL = 0,
@ -86,13 +87,20 @@ const unsigned char *find_tlv_unchecked (const unsigned char *buffer,
size_t length,
int tag, size_t *nbytes);
/* Wite a TLV header to MEMBUF. */
void put_tlv_to_membuf (membuf_t *membuf, int class, int tag,
int constructed, size_t length);
/* Count the length of a to be constructed TLV. */
size_t get_tlv_length (int class, int tag, int constructed, size_t length);
/* ASN.1 BER parser: Parse BUFFER of length SIZE and return the tag
and the length part from the TLV triplet. Update BUFFER and SIZE
on success. */
gpg_error_t parse_ber_header (unsigned char const **buffer, size_t *size,
int *r_class, int *r_tag,
int *r_constructed,
int *r_class, int *r_tag,
int *r_constructed,
int *r_ndef, size_t *r_length, size_t *r_nhdr);