1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3 #include "tomcrypt_private.h"
4
5 /**
6 @file der_encode_bit_string.c
7 ASN.1 DER, encode a BIT STRING, Tom St Denis
8 */
9
10
11 #ifdef LTC_DER
12
13 #define getbit(n, k) (((n) & ( 1 << (k) )) >> (k))
14
15 /**
16 Store a BIT STRING
17 @param in The array of bits to store (8 per char)
18 @param inlen The number of bits to store
19 @param out [out] The destination for the DER encoded BIT STRING
20 @param outlen [in/out] The max size and resulting size of the DER BIT STRING
21 @return CRYPT_OK if successful
22 */
der_encode_raw_bit_string(const unsigned char * in,unsigned long inlen,unsigned char * out,unsigned long * outlen)23 int der_encode_raw_bit_string(const unsigned char *in, unsigned long inlen,
24 unsigned char *out, unsigned long *outlen)
25 {
26 unsigned long len, x, y;
27 unsigned char buf;
28 int err;
29
30 LTC_ARGCHK(in != NULL);
31 LTC_ARGCHK(out != NULL);
32 LTC_ARGCHK(outlen != NULL);
33
34 /* avoid overflows */
35 if ((err = der_length_bit_string(inlen, &len)) != CRYPT_OK) {
36 return err;
37 }
38
39 if (len > *outlen) {
40 *outlen = len;
41 return CRYPT_BUFFER_OVERFLOW;
42 }
43
44 /* store header (include bit padding count in length) */
45 x = 0;
46 y = ((inlen + 7) >> 3) + 1;
47
48 out[x++] = 0x03;
49 len = *outlen - x;
50 if ((err = der_encode_asn1_length(y, out + x, &len)) != CRYPT_OK) {
51 return err;
52 }
53 x += len;
54
55 /* store number of zero padding bits */
56 out[x++] = (unsigned char)((8 - inlen) & 7);
57
58 /* store the bits in big endian format */
59 for (y = buf = 0; y < inlen; y++) {
60 buf |= (getbit(in[y/8],7-y%8)?1:0) << (7 - (y & 7));
61 if ((y & 7) == 7) {
62 out[x++] = buf;
63 buf = 0;
64 }
65 }
66 /* store last byte */
67 if (inlen & 7) {
68 out[x++] = buf;
69 }
70
71 *outlen = x;
72 return CRYPT_OK;
73 }
74
75 #endif
76