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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;
}