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Reimplement DSA_size without crypto/asn1.

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BUG=499653

Change-Id: I16963fb198609d7fc0df6c57923cda3e13350753
Reviewed-on: https://boringssl-review.googlesource.com/6875
Reviewed-by: Adam Langley <agl@google.com>
This commit is contained in:
David Benjamin 2016-01-02 14:35:47 -08:00 committed by Adam Langley
parent fda22a7573
commit df98a7ad3a
1 changed files with 31 additions and 18 deletions
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49
crypto/dsa/dsa.c
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@ -61,7 +61,6 @@
#include <string.h>
#include <openssl/asn1.h>
#include <openssl/bn.h>
#include <openssl/dh.h>
#include <openssl/digest.h>
@ -754,24 +753,38 @@ err:
return ret;
}
/* der_len_len returns the number of bytes needed to represent a length of |len|
* in DER. */
static size_t der_len_len(size_t len) {
if (len < 0x80) {
return 1;
}
size_t ret = 1;
while (len > 0) {
ret++;
len >>= 8;
}
return ret;
}
int DSA_size(const DSA *dsa) {
int ret, i;
ASN1_INTEGER bs;
unsigned char buf[4]; /* 4 bytes looks really small.
However, i2d_ASN1_INTEGER() will not look
beyond the first byte, as long as the second
parameter is NULL. */
i = BN_num_bits(dsa->q);
bs.length = (i + 7) / 8;
bs.data = buf;
bs.type = V_ASN1_INTEGER;
/* If the top bit is set the asn1 encoding is 1 larger. */
buf[0] = 0xff;
i = i2d_ASN1_INTEGER(&bs, NULL);
i += i; /* r and s */
ret = ASN1_object_size(1, i, V_ASN1_SEQUENCE);
size_t order_len = BN_num_bytes(dsa->q);
/* Compute the maximum length of an |order_len| byte integer. Defensively
* assume that the leading 0x00 is included. */
size_t integer_len = 1 /* tag */ + der_len_len(order_len + 1) + 1 + order_len;
if (integer_len < order_len) {
return 0;
}
/* A DSA signature is two INTEGERs. */
size_t value_len = 2 * integer_len;
if (value_len < integer_len) {
return 0;
}
/* Add the header. */
size_t ret = 1 /* tag */ + der_len_len(value_len) + value_len;
if (ret < value_len) {
return 0;
}
return ret;
}