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DPP: Use ECDH from crypto.h

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Use crypto.h API to implement ECDH in DPP. This needs a new
initialization function in crypto.h to initialize an ECDH with a given
EC key.

Using crypto_ecdh_set_peerkey() to generate the ECDH secret in an
intermediate and dynamically allocated buffer removed the need for the
DPP-specific workaround for inconsistent length returned by
EVP_PKEY_derive() since that crypto_ecdh_set_peerkey() implementation
already had functionality for covering the changing secret_len value
from commit d001fe31ab ("OpenSSL: Handle EVP_PKEY_derive() secret_len
changes for ECDH").

Signed-off-by: Cedric Izoard <cedric.izoard@ceva-dsp.com>
This commit is contained in:
Cedric Izoard 2021-10-29 11:05:31 +02:00 committed by Jouni Malinen
parent 4aed5668b4
commit e9f8f81a82
3 changed files with 69 additions and 70 deletions
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77
src/common/dpp_crypto.c
View file

@ -566,84 +566,45 @@ int dpp_derive_bk_ke(struct dpp_authentication *auth)
int dpp_ecdh(struct crypto_ec_key *own, struct crypto_ec_key *peer,
u8 *secret, size_t *secret_len)
{
EVP_PKEY_CTX *ctx;
struct crypto_ecdh *ecdh;
struct wpabuf *peer_pub, *secret_buf = NULL;
int ret = -1;
ERR_clear_error();
*secret_len = 0;
ctx = EVP_PKEY_CTX_new((EVP_PKEY *) own, NULL);
if (!ctx) {
wpa_printf(MSG_ERROR, "DPP: EVP_PKEY_CTX_new failed: %s",
ERR_error_string(ERR_get_error(), NULL));
ecdh = crypto_ecdh_init2(crypto_ec_key_group(own), own);
if (!ecdh) {
wpa_printf(MSG_ERROR, "DPP: crypto_ecdh_init2() failed");
return -1;
}
if (EVP_PKEY_derive_init(ctx) != 1) {
wpa_printf(MSG_ERROR, "DPP: EVP_PKEY_derive_init failed: %s",
ERR_error_string(ERR_get_error(), NULL));
goto fail;
}
if (EVP_PKEY_derive_set_peer(ctx, (EVP_PKEY *) peer) != 1) {
peer_pub = crypto_ec_key_get_pubkey_point(peer, 0);
if (!peer_pub) {
wpa_printf(MSG_ERROR,
"DPP: EVP_PKEY_derive_set_peet failed: %s",
ERR_error_string(ERR_get_error(), NULL));
"DPP: crypto_ec_key_get_pubkey_point() failed");
goto fail;
}
if (EVP_PKEY_derive(ctx, NULL, secret_len) != 1) {
wpa_printf(MSG_ERROR, "DPP: EVP_PKEY_derive(NULL) failed: %s",
ERR_error_string(ERR_get_error(), NULL));
secret_buf = crypto_ecdh_set_peerkey(ecdh, 1, wpabuf_head(peer_pub),
wpabuf_len(peer_pub));
if (!secret_buf) {
wpa_printf(MSG_ERROR, "DPP: crypto_ecdh_set_peerkey() failed");
goto fail;
}
if (*secret_len > DPP_MAX_SHARED_SECRET_LEN) {
u8 buf[200];
int level = *secret_len > 200 ? MSG_ERROR : MSG_DEBUG;
/* It looks like OpenSSL can return unexpectedly large buffer
* need for shared secret from EVP_PKEY_derive(NULL) in some
* cases. For example, group 19 has shown cases where secret_len
* is set to 72 even though the actual length ends up being
* updated to 32 when EVP_PKEY_derive() is called with a buffer
* for the value. Work around this by trying to fetch the value
* and continue if it is within supported range even when the
* initial buffer need is claimed to be larger. */
wpa_printf(level,
"DPP: Unexpected secret_len=%d from EVP_PKEY_derive()",
(int) *secret_len);
if (*secret_len > 200)
goto fail;
if (EVP_PKEY_derive(ctx, buf, secret_len) != 1) {
wpa_printf(MSG_ERROR, "DPP: EVP_PKEY_derive failed: %s",
ERR_error_string(ERR_get_error(), NULL));
goto fail;
}
if (*secret_len > DPP_MAX_SHARED_SECRET_LEN) {
wpa_printf(MSG_ERROR,
"DPP: Unexpected secret_len=%d from EVP_PKEY_derive()",
(int) *secret_len);
goto fail;
}
wpa_hexdump_key(MSG_DEBUG, "DPP: Unexpected secret_len change",
buf, *secret_len);
os_memcpy(secret, buf, *secret_len);
forced_memzero(buf, sizeof(buf));
goto done;
}
if (EVP_PKEY_derive(ctx, secret, secret_len) != 1) {
wpa_printf(MSG_ERROR, "DPP: EVP_PKEY_derive failed: %s",
ERR_error_string(ERR_get_error(), NULL));
if (wpabuf_len(secret_buf) > DPP_MAX_SHARED_SECRET_LEN) {
wpa_printf(MSG_ERROR, "DPP: ECDH secret longer than expected");
goto fail;
}
done:
*secret_len = wpabuf_len(secret_buf);
os_memcpy(secret, wpabuf_head(secret_buf), wpabuf_len(secret_buf));
ret = 0;
fail:
EVP_PKEY_CTX_free(ctx);
wpabuf_clear_free(secret_buf);
wpabuf_free(peer_pub);
crypto_ecdh_deinit(ecdh);
return ret;
}

36
src/crypto/crypto.h
View file

@ -945,7 +945,15 @@ void crypto_ec_point_debug_print(const struct crypto_ec *e,
const char *title);
/**
* struct crypto_ecdh - Elliptic curve Diffie–Hellman context
* struct crypto_ec_key - Elliptic curve key pair
*
* Internal data structure for EC key pair. The contents is specific to the used
* crypto library.
*/
struct crypto_ec_key;
/**
* struct crypto_ecdh - Elliptic Curve Diffie–Hellman context
*
* Internal data structure for ECDH. The contents is specific to the used
* crypto library.
@ -956,13 +964,25 @@ struct crypto_ecdh;
* crypto_ecdh_init - Initialize elliptic curve Diffie–Hellman context
* @group: Identifying number for the ECC group (IANA "Group Description"
* attribute registry for RFC 2409)
* This function generates an ephemeral key pair.
* Returns: Pointer to ECDH context or %NULL on failure
*/
struct crypto_ecdh * crypto_ecdh_init(int group);
/**
* crypto_ecdh_init2 - Initialize elliptic curve Diffie–Hellman context with a
* given EC key
* @group: Identifying number for the ECC group (IANA "Group Description"
* attribute registry for RFC 2409)
* @own_key: Our own EC Key
* Returns: Pointer to ECDH context or %NULL on failure
*/
struct crypto_ecdh * crypto_ecdh_init2(int group,
struct crypto_ec_key *own_key);
/**
* crypto_ecdh_get_pubkey - Retrieve public key from ECDH context
* @ecdh: ECDH context from crypto_ecdh_init()
* @ecdh: ECDH context from crypto_ecdh_init() or crypto_ecdh_init2()
* @inc_y: Whether public key should include y coordinate (explicit form)
* or not (compressed form)
* Returns: Binary data f the public key or %NULL on failure
@ -971,7 +991,7 @@ struct wpabuf * crypto_ecdh_get_pubkey(struct crypto_ecdh *ecdh, int inc_y);
/**
* crypto_ecdh_set_peerkey - Compute ECDH secret
* @ecdh: ECDH context from crypto_ecdh_init()
* @ecdh: ECDH context from crypto_ecdh_init() or crypto_ecdh_init2()
* @inc_y: Whether peer's public key includes y coordinate (explicit form)
* or not (compressed form)
* @key: Binary data of the peer's public key
@ -983,7 +1003,7 @@ struct wpabuf * crypto_ecdh_set_peerkey(struct crypto_ecdh *ecdh, int inc_y,
/**
* crypto_ecdh_deinit - Free ECDH context
* @ecdh: ECDH context from crypto_ecdh_init()
* @ecdh: ECDH context from crypto_ecdh_init() or crypto_ecdh_init2()
*/
void crypto_ecdh_deinit(struct crypto_ecdh *ecdh);
@ -994,14 +1014,6 @@ void crypto_ecdh_deinit(struct crypto_ecdh *ecdh);
*/
size_t crypto_ecdh_prime_len(struct crypto_ecdh *ecdh);
/**
* struct crypto_ec_key - Elliptic curve key pair
*
* Internal data structure for EC key pair. The contents is specific to the used
* crypto library.
*/
struct crypto_ec_key;
/**
* crypto_ec_key_parse_priv - Initialize EC key pair from ECPrivateKey ASN.1
* @der: DER encoding of ASN.1 ECPrivateKey

26
src/crypto/crypto_openssl.c
View file

@ -2085,6 +2085,32 @@ fail:
}
struct crypto_ecdh * crypto_ecdh_init2(int group, struct crypto_ec_key *own_key)
{
struct crypto_ecdh *ecdh;
ecdh = os_zalloc(sizeof(*ecdh));
if (!ecdh)
goto fail;
ecdh->ec = crypto_ec_init(group);
if (!ecdh->ec)
goto fail;
ecdh->pkey = EVP_PKEY_new();
if (!ecdh->pkey ||
EVP_PKEY_assign_EC_KEY(ecdh->pkey,
EVP_PKEY_get1_EC_KEY((EVP_PKEY *) own_key))
!= 1)
goto fail;
return ecdh;
fail:
crypto_ecdh_deinit(ecdh);
return NULL;
}
struct wpabuf * crypto_ecdh_get_pubkey(struct crypto_ecdh *ecdh, int inc_y)
{
struct wpabuf *buf = NULL;