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dpp-util: add dpp_point_from_asn1()

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Given an ASN1 blob of the right form, parse and create
an l_ecc_point object. The form used is specific to DPP
hence why this isn't general purpose and put into dpp-util.
This commit is contained in:
James Prestwood 2022-01-20 15:44:06 -08:00 committed by Denis Kenzior
parent dfaf6e045f
commit d8116e8828
2 changed files with 70 additions and 0 deletions
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69
src/dpp-util.c
View File

@ -796,3 +796,72 @@ uint8_t *dpp_point_to_asn1(const struct l_ecc_point *p, size_t *len_out)
return asn1;
}
/*
* Only checking for the ASN.1 form:
*
* SEQUENCE {
* SEQUENCE {
* OBJECT IDENTIFIER ecPublicKey
* OBJECT IDENTIFIER key type (p256/p384)
* }
* BITSTRING (key data)
* }
*/
struct l_ecc_point *dpp_point_from_asn1(const uint8_t *asn1, size_t len)
{
const uint8_t *outer_seq;
size_t outer_len;
const uint8_t *inner_seq;
size_t inner_len;
const uint8_t *elem;
const uint8_t *key_data;
size_t elen = 0;
uint8_t tag;
unsigned int curve_num;
const struct l_ecc_curve *curve;
/* SEQUENCE */
outer_seq = asn1_der_find_elem(asn1, len, 0, &tag, &outer_len);
if (!outer_seq || tag != ASN1_ID_SEQUENCE)
return NULL;
/* SEQUENCE */
inner_seq = asn1_der_find_elem(outer_seq, outer_len, 0, &tag, &inner_len);
if (!inner_seq || tag != ASN1_ID_SEQUENCE)
return NULL;
/* OBJECT IDENTIFIER (ecPublicKey) */
elem = asn1_der_find_elem(inner_seq, inner_len, 0, &tag, &elen);
if (!elem || tag != ASN1_ID_OID)
return NULL;
/* Check that this OID is ecPublicKey */
if (!asn1_oid_eq(&ec_oid, elen, elem))
return NULL;
elem = asn1_der_find_elem(inner_seq, inner_len, 1, &tag, &elen);
if (!elem || tag != ASN1_ID_OID)
return NULL;
/* Check if ELL supports this curve */
if (asn1_oid_eq(&ec_p256_oid, elen, elem))
curve_num = 19;
else if (asn1_oid_eq(&ec_p384_oid, elen, elem))
curve_num = 20;
else
return NULL;
curve = l_ecc_curve_from_ike_group(curve_num);
if (!curve)
return NULL;
/* BITSTRING */
key_data = asn1_der_find_elem(outer_seq, outer_len, 1, &tag, &elen);
if (!key_data || tag != ASN1_ID_BIT_STRING || elen > 2)
return NULL;
return l_ecc_point_from_data(curve, key_data[1],
key_data + 2, elen - 2);
}

1
src/dpp-util.h
View File

@ -167,3 +167,4 @@ bool dpp_derive_ke(const uint8_t *i_nonce, const uint8_t *r_nonce,
void *ke);
uint8_t *dpp_point_to_asn1(const struct l_ecc_point *p, size_t *len_out);
struct l_ecc_point *dpp_point_from_asn1(const uint8_t *asn1, size_t len);