Add demo for EC keygen

Fixes #14112

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15423)

demos/README.txt

@@ -16,6 +16,9 @@ EVP_MD_demo.c      Compute a digest from multiple buffers
 EVP_MD_stdin.c         Compute a digest with data read from stdin
 EVP_f_md.c             Compute a digest using BIO and EVP_f_md
 
+pkey:
+EVP_PKEY_EC_keygen.c   Generate an EC key.
+
 smime:
 
 pkcs12:

demos/pkey/EVP_PKEY_EC_keygen.c

@@ -0,0 +1,155 @@
+/*-
+ * Copyright 2021 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
+ */
+
+/*
+ * Example showing how to generate an EC key and extract values from the
+ * generated key.
+ */
+
+#include <string.h>
+#include <stdio.h>
+#include <openssl/err.h>
+#include <openssl/evp.h>
+#include <openssl/core_names.h>
+
+static int get_key_values(EVP_PKEY *pkey);
+
+/*
+ * The following code shows how to generate an EC key from a curve name
+ * with additional parameters. If only the curve name is required then the
+ * simple helper can be used instead i.e. Either
+ * pkey = EVP_EC_gen(curvename); OR
+ * pkey = EVP_PKEY_Q_keygen(libctx, propq, "EC", curvename);
+ */
+static EVP_PKEY *do_ec_keygen(void)
+{
+    /*
+     * The libctx and propq can be set if required, they are included here
+     * to show how they are passed to EVP_PKEY_CTX_new_from_name().
+     */
+    OSSL_LIB_CTX *libctx = NULL;
+    const char *propq = NULL;
+    EVP_PKEY *key = NULL;
+    OSSL_PARAM params[3];
+    EVP_PKEY_CTX *genctx = NULL;
+    const char *curvename = "P-256";
+    int use_cofactordh = 1;
+
+    genctx = EVP_PKEY_CTX_new_from_name(libctx, "EC", propq);
+    if (genctx == NULL) {
+        fprintf(stderr, "EVP_PKEY_CTX_new_from_name() failed\n");
+        goto cleanup;
+    }
+
+    if (EVP_PKEY_keygen_init(genctx) <= 0) {
+        fprintf(stderr, "EVP_PKEY_keygen_init() failed\n");
+        goto cleanup;
+    }
+
+    params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME,
+                                                 (char *)curvename, 0);
+    /*
+     * This is an optional parameter.
+     * For many curves where the cofactor is 1, setting this has no effect.
+     */
+    params[1] = OSSL_PARAM_construct_int(OSSL_PKEY_PARAM_USE_COFACTOR_ECDH,
+                                         &use_cofactordh);
+    params[2] = OSSL_PARAM_construct_end();
+    if (!EVP_PKEY_CTX_set_params(genctx, params)) {
+        fprintf(stderr, "EVP_PKEY_CTX_set_params() failed\n");
+        goto cleanup;
+    }
+
+    fprintf(stdout, "Generating EC key\n\n");
+    if (EVP_PKEY_generate(genctx, &key) <= 0) {
+        fprintf(stderr, "EVP_PKEY_generate() failed\n");
+        goto cleanup;
+    }
+cleanup:
+    EVP_PKEY_CTX_free(genctx);
+    return key;
+}
+
+/*
+ * The following code shows how retrieve key data from the generated
+ * EC key. See doc/man7/EVP_PKEY-EC.pod for more information.
+ *
+ * EVP_PKEY_print_private() could also be used to display the values.
+ */
+static int get_key_values(EVP_PKEY *pkey)
+{
+    int result = 0;
+    char out_curvename[80];
+    unsigned char out_pubkey[80];
+    unsigned char out_privkey[80];
+    BIGNUM *out_priv = NULL;
+    size_t i, out_pubkey_len, out_privkey_len = 0;
+
+    if (!EVP_PKEY_get_utf8_string_param(pkey, OSSL_PKEY_PARAM_GROUP_NAME,
+                                        out_curvename, sizeof(out_curvename),
+                                        NULL)) {
+        fprintf(stderr, "Failed to get curve name\n");
+        goto cleanup;
+    }
+
+    if (!EVP_PKEY_get_octet_string_param(pkey, OSSL_PKEY_PARAM_PUB_KEY,
+                                        out_pubkey, sizeof(out_pubkey),
+                                        &out_pubkey_len)) {
+        fprintf(stderr, "Failed to get public key\n");
+        goto cleanup;
+    }
+
+    if (!EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_PRIV_KEY, &out_priv)) {
+        fprintf(stderr, "Failed to get private key\n");
+        goto cleanup;
+    }
+
+    out_privkey_len = BN_bn2bin(out_priv, out_privkey);
+    if (out_privkey_len <= 0 || out_privkey_len > sizeof(out_privkey)) {
+        fprintf(stderr, "BN_bn2bin failed\n");
+        goto cleanup;
+    }
+
+    fprintf(stdout, "Curve name: %s\n", out_curvename);
+    fprintf(stdout, "Public key:\n");
+    BIO_dump_indent_fp(stdout, out_pubkey, out_pubkey_len, 2);
+    fprintf(stdout, "Private Key:\n");
+    BIO_dump_indent_fp(stdout, out_privkey, out_privkey_len, 2);
+
+    result = 1;
+cleanup:
+    /* Zeroize the private key data when we free it */
+    BN_clear_free(out_priv);
+    return result;
+}
+
+int main(void)
+{
+    int result = 0;
+    EVP_PKEY *pkey;
+
+    pkey = do_ec_keygen();
+    if (pkey == NULL)
+        goto cleanup;
+
+    if (!get_key_values(pkey))
+        goto cleanup;
+
+    /*
+     * At this point we can write out the generated key using
+     * i2d_PrivateKey() and i2d_PublicKey() if required.
+     */
+    result = 1;
+cleanup:
+    if (result != 1)
+        ERR_print_errors_fp(stderr);
+
+    EVP_PKEY_free(pkey);
+    return result == 0;
+}

demos/pkey/Makefile

@@ -0,0 +1,20 @@
+#
+# To run the demos when linked with a shared library (default):
+#
+#    LD_LIBRARY_PATH=../.. ./EVP_PKEY_EC_keygen
+
+CFLAGS = -I../../include -g
+LDFLAGS = -L../..
+LDLIBS = -lcrypto
+
+all: EVP_PKEY_EC_keygen
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $<
+
+EVP_PKEY_EC_keygen: EVP_PKEY_EC_keygen.o
+
+test: ;
+
+clean:
+	$(RM) *.o EVP_PKEY_EC_keygen