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dpp-util: add dpp_point_to_asn1

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Converts an l_ecc_point to the DPP ASN.1 structure.
This commit is contained in:
James Prestwood 2021-12-16 10:08:45 -08:00 committed by Denis Kenzior
parent 484dea8d7a
commit 5ab6566a3b
2 changed files with 92 additions and 0 deletions
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90
src/dpp-util.c
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@ -361,3 +361,93 @@ bool dpp_derive_ke(const uint8_t *i_nonce, const uint8_t *r_nonce,
/* ke = HKDF-Expand(bk, "DPP Key", length) */
return hkdf_expand(sha, bk, key_len, "DPP Key", ke, key_len);
}
#define ASN1_ID(class, pc, tag) (((class) << 6) | ((pc) << 5) | (tag))
#define ASN1_ID_SEQUENCE ASN1_ID(0, 1, 0x10)
#define ASN1_ID_BIT_STRING ASN1_ID(0, 0, 0x03)
#define ASN1_ID_OID ASN1_ID(0, 0, 0x06)
/*
* Values derived from OID definitions in https://www.secg.org/sec2-v2.pdf
* Appendix A.2.1
*
* 1.2.840.10045.2.1 (ecPublicKey)
*/
static uint8_t ec_oid[] = { 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01 };
/* 1.2.840.10045.3.1.7 (prime256v1) */
static uint8_t ec_p256_oid[] = { 0x2a, 0x86, 0x48, 0xce,
0x3d, 0x03, 0x01, 0x07 };
/* 1.3.132.0.34 (secp384r1) */
static uint8_t ec_p384_oid[] = { 0x2B, 0x81, 0x04, 0x00, 0x22 };
uint8_t *dpp_point_to_asn1(const struct l_ecc_point *p, size_t *len_out)
{
uint8_t *asn1;
uint8_t *ptr;
uint8_t *type_oid;
size_t type_oid_len;
const struct l_ecc_curve *curve = l_ecc_point_get_curve(p);
ssize_t key_size = l_ecc_curve_get_scalar_bytes(curve);
uint64_t x[L_ECC_MAX_DIGITS];
ssize_t ret;
size_t len;
switch (key_size) {
case 32:
type_oid = ec_p256_oid;
type_oid_len = sizeof(ec_p256_oid);
break;
case 48:
type_oid = ec_p384_oid;
type_oid_len = sizeof(ec_p384_oid);
break;
default:
return NULL;
}
ret = l_ecc_point_get_x(p, x, sizeof(x));
if (ret < 0 || ret != key_size)
return NULL;
len = 2 + sizeof(ec_oid) + 2 + type_oid_len + 2 + key_size + 4;
if (L_WARN_ON(len > 128))
return NULL;
asn1 = l_malloc(len + 2);
ptr = asn1;
*ptr++ = ASN1_ID_SEQUENCE;
/* Length of both OIDs and key, plus tag/len bytes */
*ptr++ = len;
*ptr++ = ASN1_ID_SEQUENCE;
len = sizeof(ec_oid) + type_oid_len + 4;
*ptr++ = len;
*ptr++ = ASN1_ID_OID;
*ptr++ = sizeof(ec_oid);
memcpy(ptr, ec_oid, sizeof(ec_oid));
ptr += sizeof(ec_oid);
*ptr++ = ASN1_ID_OID;
*ptr++ = type_oid_len;
memcpy(ptr, type_oid, type_oid_len);
ptr += type_oid_len;
*ptr++ = ASN1_ID_BIT_STRING;
*ptr++ = key_size + 2;
*ptr++ = 0x00;
*ptr++ = 0x03;
memcpy(ptr, x, key_size);
ptr += key_size;
if (len_out)
*len_out = ptr - asn1;
return asn1;
}

2
src/dpp-util.h
View File

@ -137,3 +137,5 @@ struct l_ecc_scalar *dpp_derive_k2(const struct l_ecc_point *i_proto_public,
bool dpp_derive_ke(const uint8_t *i_nonce, const uint8_t *r_nonce,
struct l_ecc_scalar *m, struct l_ecc_scalar *n,
void *ke);
uint8_t *dpp_point_to_asn1(const struct l_ecc_point *p, size_t *len_out);