Converts an l_ecc_point to the DPP ASN.1 structure. --- src/dpp-util.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++ src/dpp-util.h | 2 ++ 2 files changed, 91 insertions(+) diff --git a/src/dpp-util.c b/src/dpp-util.c index 0b355311..e5f76bfd 100644 --- a/src/dpp-util.c +++ b/src/dpp-util.c @@ -361,3 +361,92 @@ 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) + +static uint8_t ec_oid[] = { 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01 }; +static uint8_t ec_p256_oid[] = { 0x2a, 0x86, 0x48, 0xce, + 0x3d, 0x03, 0x01, 0x07 }; +static uint8_t ec_p384_oid[] = { 0x2B, 0x81, 0x04, 0x00, 0x22 }; +static uint8_t ec_p512_oid[] = { 0x2B, 0x81, 0x04, 0x00, 0x23 }; + +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; + case 64: + type_oid = ec_p512_oid; + type_oid_len = sizeof(ec_p512_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; + + if (L_WARN_ON(len > 128)) + return NULL; + + *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; +} diff --git a/src/dpp-util.h b/src/dpp-util.h index 6d0dcccb..0c22e9b7 100644 --- a/src/dpp-util.h +++ b/src/dpp-util.h @@ -97,3 +97,5 @@ 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); -- 2.31.1