--- /dev/null
+/*
+ * Copyright 2023 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License"). You may not use
+ * this file except in compliance with the License. You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <openssl/core_names.h>
+#include <openssl/evp.h>
+#include <openssl/err.h>
+
+/*
+ * This is a demonstration of key exchange using ECDH.
+ *
+ * EC key exchange requires 2 parties (peers) to first agree on shared group
+ * parameters (the EC curve name). Each peer then generates a public/private
+ * key pair using the shared curve name. Each peer then gives their public key
+ * to the other peer. A peer can then derive the same shared secret using their
+ * private key and the other peers public key.
+ */
+
+/* Object used to store information for a single Peer */
+typedef struct peer_data_st {
+ const char *name; /* name of peer */
+ const char *curvename; /* The shared curve name */
+ EVP_PKEY *priv; /* private keypair */
+ EVP_PKEY *pub; /* public key to send to other peer */
+ unsigned char *secret; /* allocated shared secret buffer */
+ size_t secretlen;
+} PEER_DATA;
+
+/*
+ * The public key needs to be given to the other peer
+ * The following code extracts the public key data from the private key
+ * and then builds an EVP_KEY public key.
+ */
+static int get_peer_public_key(PEER_DATA *peer, OSSL_LIB_CTX *libctx)
+{
+ int ret = 0;
+ EVP_PKEY_CTX *ctx;
+ OSSL_PARAM params[3];
+ unsigned char pubkeydata[256];
+ size_t pubkeylen;
+
+ /* Get the EC encoded public key data from the peers private key */
+ if (!EVP_PKEY_get_octet_string_param(peer->priv, OSSL_PKEY_PARAM_PUB_KEY,
+ pubkeydata, sizeof(pubkeydata),
+ &pubkeylen))
+ return 0;
+
+ /* Create a EC public key from the public key data */
+ ctx = EVP_PKEY_CTX_new_from_name(libctx, "EC", NULL);
+ if (ctx == NULL)
+ return 0;
+ params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME,
+ (char *)peer->curvename, 0);
+ params[1] = OSSL_PARAM_construct_octet_string(OSSL_PKEY_PARAM_PUB_KEY,
+ pubkeydata, pubkeylen);
+ params[2] = OSSL_PARAM_construct_end();
+ ret = EVP_PKEY_fromdata_init(ctx) > 0
+ && (EVP_PKEY_fromdata(ctx, &peer->pub, EVP_PKEY_PUBLIC_KEY,
+ params) > 0);
+ EVP_PKEY_CTX_free(ctx);
+ return ret;
+}
+
+static int create_peer(PEER_DATA *peer, OSSL_LIB_CTX *libctx)
+{
+ int ret = 0;
+ EVP_PKEY_CTX *ctx = NULL;
+ OSSL_PARAM params[2];
+
+ params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME,
+ (char *)peer->curvename, 0);
+ params[1] = OSSL_PARAM_construct_end();
+
+ ctx = EVP_PKEY_CTX_new_from_name(libctx, "EC", NULL);
+ if (ctx == NULL)
+ return 0;
+
+ if (EVP_PKEY_keygen_init(ctx) <= 0
+ || !EVP_PKEY_CTX_set_params(ctx, params)
+ || EVP_PKEY_generate(ctx, &peer->priv) <= 0
+ || !get_peer_public_key(peer, libctx)) {
+ EVP_PKEY_free(peer->priv);
+ peer->priv = NULL;
+ goto err;
+ }
+ ret = 1;
+err:
+ EVP_PKEY_CTX_free(ctx);
+ return ret;
+}
+
+static void destroy_peer(PEER_DATA *peer)
+{
+ EVP_PKEY_free(peer->priv);
+ EVP_PKEY_free(peer->pub);
+}
+
+static int generate_secret(PEER_DATA *peerA, EVP_PKEY *peerBpub,
+ OSSL_LIB_CTX *libctx)
+{
+ unsigned char *secret = NULL;
+ size_t secretlen = 0;
+ EVP_PKEY_CTX *derivectx;
+
+ /* Create an EVP_PKEY_CTX that contains peerA's private key */
+ derivectx = EVP_PKEY_CTX_new_from_pkey(libctx, peerA->priv, NULL);
+ if (derivectx == NULL)
+ return 0;
+
+ if (EVP_PKEY_derive_init(derivectx) <= 0)
+ goto cleanup;
+ /* Set up peerB's public key */
+ if (EVP_PKEY_derive_set_peer(derivectx, peerBpub) <= 0)
+ goto cleanup;
+
+ /*
+ * For backwards compatibility purposes the OpenSSL ECDH provider supports
+ * optionally using a X963KDF to expand the secret data. This can be done
+ * with code similar to the following.
+ *
+ * OSSL_PARAM params[5];
+ * size_t outlen = 128;
+ * unsigned char ukm[] = { 1, 2, 3, 4 };
+ * params[0] = OSSL_PARAM_construct_utf8_string(OSSL_EXCHANGE_PARAM_KDF_TYPE,
+ * "X963KDF", 0);
+ * params[1] = OSSL_PARAM_construct_utf8_string(OSSL_EXCHANGE_PARAM_KDF_DIGEST,
+ * "SHA256", 0);
+ * params[2] = OSSL_PARAM_construct_size_t(OSSL_EXCHANGE_PARAM_KDF_OUTLEN,
+ * &outlen);
+ * params[3] = OSSL_PARAM_construct_octet_string(OSSL_EXCHANGE_PARAM_KDF_UKM,
+ * ukm, sizeof(ukm));
+ * params[4] = OSSL_PARAM_construct_end();
+ * if (!EVP_PKEY_CTX_set_params(derivectx, params))
+ * goto cleanup;
+ *
+ * Note: After the secret is generated below, the peer could alternatively
+ * pass the secret to a KDF to derive additional key data from the secret.
+ * See demos/kdf/hkdf.c for an example (where ikm is the secret key)
+ */
+
+ /* Calculate the size of the secret and allocate space */
+ if (EVP_PKEY_derive(derivectx, NULL, &secretlen) <= 0)
+ goto cleanup;
+ secret = (unsigned char *)OPENSSL_malloc(secretlen);
+ if (secret == NULL)
+ goto cleanup;
+
+ /*
+ * Derive the shared secret. In this example 32 bytes are generated.
+ * For EC curves the secret size is related to the degree of the curve
+ * which is 256 bits for P-256.
+ */
+ if (EVP_PKEY_derive(derivectx, secret, &secretlen) <= 0)
+ goto cleanup;
+ peerA->secret = secret;
+ peerA->secretlen = secretlen;
+
+ printf("Shared secret (%s):\n", peerA->name);
+ BIO_dump_indent_fp(stdout, peerA->secret, peerA->secretlen, 2);
+ putchar('\n');
+
+ return 1;
+cleanup:
+ OPENSSL_free(secret);
+ EVP_PKEY_CTX_free(derivectx);
+ return 0;
+}
+
+int main(void)
+{
+ int ret = EXIT_FAILURE;
+ /* Initialise the 2 peers that will share a secret */
+ PEER_DATA peer1 = {"peer 1", "P-256"};
+ PEER_DATA peer2 = {"peer 2", "P-256"};
+ /*
+ * Setting libctx to NULL uses the default library context
+ * Use OSSL_LIB_CTX_new() to create a non default library context
+ */
+ OSSL_LIB_CTX *libctx = NULL;
+
+ /* Each peer creates a (Ephemeral) keypair */
+ if (!create_peer(&peer1, libctx)
+ || !create_peer(&peer2, libctx)) {
+ fprintf(stderr, "Create peer failed\n");
+ goto cleanup;
+ }
+
+ /*
+ * Each peer uses its private key and the other peers public key to
+ * derive a shared secret
+ */
+ if (!generate_secret(&peer1, peer2.pub, libctx)
+ || !generate_secret(&peer2, peer1.pub, libctx)) {
+ fprintf(stderr, "Generate secrets failed\n");
+ goto cleanup;
+ }
+
+ /* For illustrative purposes demonstrate that the derived secrets are equal */
+ if (peer1.secretlen != peer2.secretlen
+ || CRYPTO_memcmp(peer1.secret, peer2.secret, peer1.secretlen) != 0) {
+ fprintf(stderr, "Derived secrets do not match\n");
+ goto cleanup;
+ } else {
+ fprintf(stdout, "Derived secrets match\n");
+ }
+
+ ret = EXIT_SUCCESS;
+cleanup:
+ if (ret != EXIT_SUCCESS)
+ ERR_print_errors_fp(stderr);
+ destroy_peer(&peer2);
+ destroy_peer(&peer1);
+ return ret;
+}
projects / thirdparty / openssl.git / commitdiff
