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hostapd: fix OWE association with mbedtls

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The code for hostapd-mbedtls did not work when used for OWE association.

When handling association requests, the buffer offsets and length
assumptions were incorrect, leading to never calculating the y point,
thus denying association.

Also when crafting the association response, the buffer contained the
trailing key-type.

Fix up both issues to adhere to the specification and make
hostapd-mbedtls work with the OWE security type.
This commit is contained in:
David Bauer 2023-10-24 03:07:48 +02:00 • committed by sinavir
parent da1c0bb385
commit 09d6720d6d
No known key found for this signature in database
1 changed files with 21 additions and 20 deletions
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41
src/crypto/crypto_mbedtls.c
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@ -2299,25 +2299,30 @@ struct crypto_ecdh * crypto_ecdh_init2(int group,
struct wpabuf * crypto_ecdh_get_pubkey(struct crypto_ecdh *ecdh, int inc_y) struct wpabuf * crypto_ecdh_get_pubkey(struct crypto_ecdh *ecdh, int inc_y)
{ {
mbedtls_ecp_group *grp = &ecdh->grp; mbedtls_ecp_group *grp = &ecdh->grp;
size_t len = CRYPTO_EC_plen(grp); size_t prime_len = CRYPTO_EC_plen(grp);
size_t output_len = prime_len;
u8 output_offset = 0;
u8 buf[256];
#ifdef MBEDTLS_ECP_MONTGOMERY_ENABLED #ifdef MBEDTLS_ECP_MONTGOMERY_ENABLED
/* len */ /* len */
#endif #endif
#ifdef MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED #ifdef MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED
if (mbedtls_ecp_get_type(grp) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS) if (mbedtls_ecp_get_type(grp) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS) {
len = inc_y ? len*2+1 : len+1; output_len = inc_y ? prime_len * 2 + 1 : prime_len + 1;
output_offset = 1;
}
#endif #endif
struct wpabuf *buf = wpabuf_alloc(len);
if (buf == NULL) if (output_len > sizeof(buf))
return NULL; return NULL;
inc_y = inc_y ? MBEDTLS_ECP_PF_UNCOMPRESSED : MBEDTLS_ECP_PF_COMPRESSED; inc_y = inc_y ? MBEDTLS_ECP_PF_UNCOMPRESSED : MBEDTLS_ECP_PF_COMPRESSED;
if (mbedtls_ecp_point_write_binary(grp, &ecdh->Q, inc_y, &len, if (mbedtls_ecp_point_write_binary(grp, &ecdh->Q, inc_y, &output_len,
wpabuf_mhead_u8(buf), len) == 0) { buf, output_len) == 0) {
wpabuf_put(buf, len); return wpabuf_alloc_copy(buf + output_offset, output_len - output_offset);
return buf;
} }
wpabuf_free(buf);
return NULL; return NULL;
} }
@ -2379,10 +2384,7 @@ struct wpabuf * crypto_ecdh_set_peerkey(struct crypto_ecdh *ecdh, int inc_y,
os_memcpy(buf+2, key, len); os_memcpy(buf+2, key, len);
} }
len >>= 1; /*(repurpose len to prime_len)*/ len >>= 1; /*(repurpose len to prime_len)*/
} } else { /* (inc_y == 0) */
else if (key[0] == 0x02 || key[0] == 0x03) { /* (inc_y == 0) */
--len; /*(repurpose len to prime_len)*/
/* mbedtls_ecp_point_read_binary() does not currently support /* mbedtls_ecp_point_read_binary() does not currently support
* MBEDTLS_ECP_PF_COMPRESSED format (buf[1] = 0x02 or 0x03) * MBEDTLS_ECP_PF_COMPRESSED format (buf[1] = 0x02 or 0x03)
* (returns MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE) */ * (returns MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE) */
@ -2390,22 +2392,21 @@ struct wpabuf * crypto_ecdh_set_peerkey(struct crypto_ecdh *ecdh, int inc_y,
/* derive y, amend buf[] with y for UNCOMPRESSED format */ /* derive y, amend buf[] with y for UNCOMPRESSED format */
if (sizeof(buf)-2 < len*2 || len == 0) if (sizeof(buf)-2 < len*2 || len == 0)
return NULL; return NULL;
buf[0] = (u8)(1+len*2); buf[0] = (u8)(1+len*2);
buf[1] = 0x04; buf[1] = 0x04;
os_memcpy(buf+2, key, len);
mbedtls_mpi bn; mbedtls_mpi bn;
mbedtls_mpi_init(&bn); mbedtls_mpi_init(&bn);
int ret = mbedtls_mpi_read_binary(&bn, key+1, len) int ret = mbedtls_mpi_read_binary(&bn, key, len)
|| crypto_mbedtls_short_weierstrass_derive_y(grp, &bn, || crypto_mbedtls_short_weierstrass_derive_y(grp, &bn, 0)
key[0] & 1)
|| mbedtls_mpi_write_binary(&bn, buf+2+len, len); || mbedtls_mpi_write_binary(&bn, buf+2+len, len);
mbedtls_mpi_free(&bn); mbedtls_mpi_free(&bn);
if (ret != 0) if (ret != 0)
return NULL; return NULL;
} }
if (key[0] == 0) /*(repurpose len to prime_len)*/
len = CRYPTO_EC_plen(grp);
if (mbedtls_ecdh_read_public(&ecdh->ctx, buf, buf[0]+1)) if (mbedtls_ecdh_read_public(&ecdh->ctx, buf, buf[0]+1))
return NULL; return NULL;
} }