diff options
author | Hugo Landau <hlandau@openssl.org> | 2022-03-02 13:08:53 +0000 |
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committer | Pauli <pauli@openssl.org> | 2022-03-04 11:03:36 +1100 |
commit | 2cc7c9b6981d683711e76c3483f813701b686eb9 (patch) | |
tree | 1e7c5110a748a8e1624e99b7443bb26023d9bf4a /demos | |
parent | a3b4cd1d6e307c1b1607ee9270658b5baf0b9870 (diff) | |
download | openssl-2cc7c9b6981d683711e76c3483f813701b686eb9.tar.gz |
Add EVP demo for X25519 key exchange
This offers both a known answer test with fixed keys and also
demonstrates a more realistic usage with random keys.
Fixes #14118.
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17799)
Diffstat (limited to 'demos')
-rw-r--r-- | demos/keyexch/x25519.c | 278 |
1 files changed, 278 insertions, 0 deletions
diff --git a/demos/keyexch/x25519.c b/demos/keyexch/x25519.c new file mode 100644 index 0000000000..bd35e0a98c --- /dev/null +++ b/demos/keyexch/x25519.c @@ -0,0 +1,278 @@ +/* + * Copyright 2022 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> + +/* + * This is a demonstration of key exchange using X25519. + * + * The variables beginning `peer1_` / `peer2_` are data which would normally be + * accessible to that peer. + * + * Ordinarily you would use random keys, which are demonstrated + * below when use_kat=0. A known answer test is demonstrated + * when use_kat=1. + */ + +/* A property query used for selecting the X25519 implementation. */ +static const char *propq = NULL; + +static const unsigned char peer1_privk_data[32] = { + 0x80, 0x5b, 0x30, 0x20, 0x25, 0x4a, 0x70, 0x2c, + 0xad, 0xa9, 0x8d, 0x7d, 0x47, 0xf8, 0x1b, 0x20, + 0x89, 0xd2, 0xf9, 0x14, 0xac, 0x92, 0x27, 0xf2, + 0x10, 0x7e, 0xdb, 0x21, 0xbd, 0x73, 0x73, 0x5d +}; + +static const unsigned char peer2_privk_data[32] = { + 0xf8, 0x84, 0x19, 0x69, 0x79, 0x13, 0x0d, 0xbd, + 0xb1, 0x76, 0xd7, 0x0e, 0x7e, 0x0f, 0xb6, 0xf4, + 0x8c, 0x4a, 0x8c, 0x5f, 0xd8, 0x15, 0x09, 0x0a, + 0x71, 0x78, 0x74, 0x92, 0x0f, 0x85, 0xc8, 0x43 +}; + +static const unsigned char expected_result[32] = { + 0x19, 0x71, 0x26, 0x12, 0x74, 0xb5, 0xb1, 0xce, + 0x77, 0xd0, 0x79, 0x24, 0xb6, 0x0a, 0x5c, 0x72, + 0x0c, 0xa6, 0x56, 0xc0, 0x11, 0xeb, 0x43, 0x11, + 0x94, 0x3b, 0x01, 0x45, 0xca, 0x19, 0xfe, 0x09 +}; + +typedef struct peer_data_st { + const char *name; /* name of peer */ + EVP_PKEY *privk; /* privk generated for peer */ + unsigned char pubk_data[32]; /* generated pubk to send to other peer */ + + unsigned char *secret; /* allocated shared secret buffer */ + size_t secret_len; +} PEER_DATA; + +/* + * Prepare for X25519 key exchange. The public key to be sent to the remote peer + * is put in pubk_data, which should be a 32-byte buffer. Returns 1 on success. + */ +static int keyexch_x25519_before( + OSSL_LIB_CTX *libctx, + const unsigned char *kat_privk_data, + PEER_DATA *local_peer) +{ + int rv = 0; + size_t pubk_data_len = 0; + + /* Generate or load X25519 key for the peer */ + if (kat_privk_data != NULL) + local_peer->privk = + EVP_PKEY_new_raw_private_key_ex(libctx, "X25519", propq, + kat_privk_data, + sizeof(peer1_privk_data)); + else + local_peer->privk = EVP_PKEY_Q_keygen(libctx, propq, "X25519"); + + if (local_peer->privk == NULL) { + fprintf(stderr, "Could not load or generate private key\n"); + goto end; + } + + /* Get public key corresponding to the private key */ + if (EVP_PKEY_get_octet_string_param(local_peer->privk, + OSSL_PKEY_PARAM_PUB_KEY, + local_peer->pubk_data, + sizeof(local_peer->pubk_data), + &pubk_data_len) == 0) { + fprintf(stderr, "EVP_PKEY_get_octet_string_param() failed\n"); + goto end; + } + + /* X25519 public keys are always 32 bytes */ + if (pubk_data_len != 32) { + fprintf(stderr, "EVP_PKEY_get_octet_string_param() " + "yielded wrong length\n"); + goto end; + } + + rv = 1; +end: + if (rv == 0) { + EVP_PKEY_free(local_peer->privk); + local_peer->privk = NULL; + } + + return rv; +} + +/* + * Complete X25519 key exchange. remote_peer_pubk_data should be the 32 byte + * public key value received from the remote peer. On success, returns 1 and the + * secret is pointed to by *secret. The caller must free it. + */ +static int keyexch_x25519_after( + OSSL_LIB_CTX *libctx, + int use_kat, + PEER_DATA *local_peer, + const unsigned char *remote_peer_pubk_data) +{ + int rv = 0; + EVP_PKEY *remote_peer_pubk = NULL; + EVP_PKEY_CTX *ctx = NULL; + + local_peer->secret = NULL; + + /* Load public key for remote peer. */ + remote_peer_pubk = + EVP_PKEY_new_raw_public_key_ex(libctx, "X25519", propq, + remote_peer_pubk_data, 32); + if (remote_peer_pubk == NULL) { + fprintf(stderr, "EVP_PKEY_new_raw_public_key_ex() failed\n"); + goto end; + } + + /* Create key exchange context. */ + ctx = EVP_PKEY_CTX_new_from_pkey(libctx, local_peer->privk, propq); + if (ctx == NULL) { + fprintf(stderr, "EVP_PKEY_CTX_new_from_pkey() failed\n"); + goto end; + } + + /* Initialize derivation process. */ + if (EVP_PKEY_derive_init(ctx) == 0) { + fprintf(stderr, "EVP_PKEY_derive_init() failed\n"); + goto end; + } + + /* Configure each peer with the other peer's public key. */ + if (EVP_PKEY_derive_set_peer(ctx, remote_peer_pubk) == 0) { + fprintf(stderr, "EVP_PKEY_derive_set_peer() failed\n"); + goto end; + } + + /* Determine the secret length. */ + if (EVP_PKEY_derive(ctx, NULL, &local_peer->secret_len) == 0) { + fprintf(stderr, "EVP_PKEY_derive() failed\n"); + goto end; + } + + /* + * We are using X25519, so the secret generated will always be 32 bytes. + * However for exposition, the code below demonstrates a generic + * implementation for arbitrary lengths. + */ + if (local_peer->secret_len != 32) { /* unreachable */ + fprintf(stderr, "Secret is always 32 bytes for X25519\n"); + goto end; + } + + /* Allocate memory for shared secrets. */ + local_peer->secret = OPENSSL_malloc(local_peer->secret_len); + if (local_peer->secret == NULL) { + fprintf(stderr, "Could not allocate memory for secret\n"); + goto end; + } + + /* Derive the shared secret. */ + if (EVP_PKEY_derive(ctx, local_peer->secret, + &local_peer->secret_len) == 0) { + fprintf(stderr, "EVP_PKEY_derive() failed\n"); + goto end; + } + + printf("Shared secret (%s):\n", local_peer->name); + BIO_dump_indent_fp(stdout, local_peer->secret, local_peer->secret_len, 2); + putchar('\n'); + + rv = 1; +end: + EVP_PKEY_CTX_free(ctx); + EVP_PKEY_free(remote_peer_pubk); + if (rv == 0) { + OPENSSL_clear_free(local_peer->secret, local_peer->secret_len); + local_peer->secret = NULL; + } + + return rv; +} + +static int keyexch_x25519(int use_kat) +{ + int rv = 0; + OSSL_LIB_CTX *libctx = NULL; + PEER_DATA peer1 = {"peer 1"}, peer2 = {"peer 2"}; + + /* + * Each peer generates its private key and sends its public key + * to the other peer. The private key is stored locally for + * later use. + */ + if (keyexch_x25519_before(libctx, use_kat ? peer1_privk_data : NULL, + &peer1) == 0) + return 0; + + if (keyexch_x25519_before(libctx, use_kat ? peer2_privk_data : NULL, + &peer2) == 0) + return 0; + + /* + * Each peer uses the other peer's public key to perform key exchange. + * After this succeeds, each peer has the same secret in its + * PEER_DATA. + */ + if (keyexch_x25519_after(libctx, use_kat, &peer1, peer2.pubk_data) == 0) + return 0; + + if (keyexch_x25519_after(libctx, use_kat, &peer2, peer1.pubk_data) == 0) + return 0; + + /* + * Here we demonstrate the secrets are equal for exposition purposes. + * + * Although in practice you will generally not need to compare secrets + * produced through key exchange, if you do compare cryptographic secrets, + * always do so using a constant-time function such as CRYPTO_memcmp, never + * using memcmp(3). + */ + if (CRYPTO_memcmp(peer1.secret, peer2.secret, peer1.secret_len) != 0) { + fprintf(stderr, "Negotiated secrets do not match\n"); + goto end; + } + + /* If we are doing the KAT, the secret should equal our reference result. */ + if (use_kat && CRYPTO_memcmp(peer1.secret, expected_result, + peer1.secret_len) != 0) { + fprintf(stderr, "Did not get expected result\n"); + goto end; + } + + rv = 1; +end: + /* The secrets are sensitive, so ensure they are erased before freeing. */ + OPENSSL_clear_free(peer1.secret, peer1.secret_len); + OPENSSL_clear_free(peer2.secret, peer2.secret_len); + + EVP_PKEY_free(peer1.privk); + EVP_PKEY_free(peer2.privk); + OSSL_LIB_CTX_free(libctx); + return rv; +} + +int main(int argc, char **argv) +{ + /* Test X25519 key exchange with known result. */ + printf("Key exchange using known answer (deterministic):\n"); + if (keyexch_x25519(1) == 0) + return 1; + + /* Test X25519 key exchange with random keys. */ + printf("Key exchange using random keys:\n"); + if (keyexch_x25519(0) == 0) + return 1; + + return 0; +} |