Add a key generation example

Author: elichai

examples/keygen.c

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <assert.h>
+
+#include "random.h"
+#include "secp256k1.h"
+
+
+void print_hex(unsigned char* data, size_t size) {
+    size_t i;
+    printf("0x");
+    for (i = 0; i < size; i++) {
+        printf("%02x", data[i]);
+    }
+    printf("\n");
+}
+
+int main(void) {
+    unsigned char seckey[32];
+    unsigned char compressed_pubkey[33];
+    unsigned char uncompressed_pubkey[65];
+    size_t len;
+    secp256k1_pubkey pubkey;
+    secp256k1_context* ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
+    while (1) {
+        if (!fill_random(seckey, sizeof(seckey))) {
+            printf("Failed to generate randomness\n");
+                return 1;
+        }
+        if (secp256k1_ec_seckey_verify(ctx, seckey)) {
+            break;
+        }
+    }
+
+    /* Pubkey creation on a valid Context with a verified seckey should never fail */
+    assert(secp256k1_ec_pubkey_create(ctx, &pubkey, seckey));
+
+    /* Serialize the pubkey in a compressed form */
+    len = sizeof(compressed_pubkey);
+    secp256k1_ec_pubkey_serialize(ctx, compressed_pubkey, &len, &pubkey, SECP256K1_EC_COMPRESSED);
+    /* Should be the same size as the size of the output */
+    assert(len == sizeof(compressed_pubkey));
+
+    /* Serialize the pubkey in an uncompressed form */
+    len = sizeof(uncompressed_pubkey);
+    secp256k1_ec_pubkey_serialize(ctx, uncompressed_pubkey, &len, &pubkey, SECP256K1_EC_UNCOMPRESSED);
+    assert(len == sizeof(uncompressed_pubkey));
+
+    printf("Secret Key: ");
+    print_hex(seckey, sizeof(seckey));
+    printf("Compressed Pubkey: ");
+    print_hex(compressed_pubkey, sizeof(compressed_pubkey));
+    printf("Uncompressed Pubkey: ");
+    print_hex(uncompressed_pubkey, sizeof(uncompressed_pubkey));
+
+    return 0;
+}

examples/random.h

@@ -0,0 +1,31 @@
+#if defined(_WIN32)
+#include <bcrypt.h>
+#elif defined(__linux__)
+#include <fcntl.h>
+#include <unistd.h>
+#else
+#error "Couldn't identify the OS"
+#endif
+
+
+/* Returns 1 on sucess, and 0 on failure. */
+int fill_random(unsigned char* data, unsigned long size) {
+#if defined(_WIN32)
+    NTSTATUS res = BCryptGenRandom(NULL, data, size, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+    if (res != STATUS_SUCCESS) {
+        return 0;
+    }
+#elif defined(__linux__)
+    ssize_t res;
+    int fd = open("/dev/urandom", O_RDONLY);
+    if (fd == -1 ) {
+        return 0;
+    }
+    res = read(fd, data, size);
+    close(fd);
+    if (res != (ssize_t)size) {
+        return 0;
+    }
+#endif
+    return 1;
+}