Diff: main.cpp

Revision:

0:23d71aa111c7

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Sun Sep 15 17:40:28 2019 +0000
@@ -0,0 +1,132 @@
+#include "mbed.h"
+
+#include "secp256k1.h"
+#include "secp256k1_preallocated.h"
+
+RawSerial pc(SERIAL_TX, SERIAL_RX, 115200);
+
+// small helper functions that prints 
+// data in hex to the serial port
+void print_hex(const uint8_t * data, size_t data_len){
+    for(int i=0; i<data_len; i++){
+        printf("%02x", data[i]);
+    }
+}
+// just adds a new line to the end of the data
+void println_hex(const uint8_t * data, size_t data_len){
+    print_hex(data, data_len);
+    printf("\r\n");
+}
+// prints error and hangs forever
+void err(const char * message, void * data = NULL){
+    printf("ERROR: %s\r\n", message);
+    while(1){
+        wait(1);
+    }
+}
+
+void secp_example(){
+    // secp256k1 context
+    secp256k1_context *ctx = NULL;
+
+    int res;    // to store results of function calls
+    size_t len; // to store serialization lengths
+
+    printf("=== secp256k1 context ===\r\n");
+
+    // first we need to create the context
+    // this is the size of memory to be allocated
+    size_t context_size = secp256k1_context_preallocated_size(SECP256K1_CONTEXT_VERIFY | SECP256K1_CONTEXT_SIGN);
+    printf("Context size: %u bytes\r\n", context_size);
+
+    // creating the context
+    ctx = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY | SECP256K1_CONTEXT_SIGN);
+    printf("Context created\r\n");
+
+    printf("=== Secret key ===\r\n");
+    // some random secret key
+    uint8_t secret[] = {
+        0xbd, 0xb5, 0x1a, 0x16, 0xeb, 0x64, 0x60, 0xec, 
+        0x16, 0xf8, 0x4d, 0x7b, 0x6f, 0x19, 0xe2, 0x0d, 
+        0x9b, 0x9a, 0xb5, 0x58, 0xfa, 0x0e, 0x9a, 0xe4, 
+        0xbb, 0x49, 0x3e, 0xf7, 0x79, 0xf1, 0x40, 0x55
+    };
+    printf("Secret key: ");
+    println_hex(secret, sizeof(secret));
+
+    // Makes sense to check if secret key is valid.
+    // It will be ok in most cases, only if secret > N it will be invalid
+    res = secp256k1_ec_seckey_verify(ctx, secret);
+    if(!res){ err("Secret key is invalid"); }
+
+    /**************** Public key ******************/
+
+    printf("=== Public key ===\r\n");
+    // computing corresponding pubkey
+    secp256k1_pubkey pubkey;
+    res = secp256k1_ec_pubkey_create(ctx, &pubkey, secret);
+    if(!res){ err("Pubkey computation failed"); }
+
+    // serialize the pubkey in compressed format
+    uint8_t pub[33];
+    len = sizeof(pub);
+    secp256k1_ec_pubkey_serialize(ctx, pub, &len, &pubkey, SECP256K1_EC_COMPRESSED);
+    printf("Public key: ");
+    println_hex(pub, len);
+
+    // this is how you parse the pubkey
+    res = secp256k1_ec_pubkey_parse(ctx, &pubkey, pub, 33);
+    if(res){
+        printf("Key is valid\r\n");
+    }else{
+        printf("Invalid key\r\n");
+    }
+
+    /**************** Signature stuff ******************/
+
+    printf("=== Signature generation ===\r\n");
+
+    // hash of the string "hello"
+    uint8_t hash[32] = { 
+        0x2c, 0xf2, 0x4d, 0xba, 0x5f, 0xb0, 0xa3, 0x0e, 
+        0x26, 0xe8, 0x3b, 0x2a, 0xc5, 0xb9, 0xe2, 0x9e, 
+        0x1b, 0x16, 0x1e, 0x5c, 0x1f, 0xa7, 0x42, 0x5e, 
+        0x73, 0x04, 0x33, 0x62, 0x93, 0x8b, 0x98, 0x24 
+    };
+    // signing
+    secp256k1_ecdsa_signature sig;
+    res = secp256k1_ecdsa_sign(ctx, &sig, hash, secret, NULL, NULL);
+    if(!res){ err("Can't sign"); }
+
+    // serialization
+    uint8_t der[72];
+    len = sizeof(der);
+    res = secp256k1_ecdsa_signature_serialize_der(ctx, der, &len, &sig);
+    if(!res){ err("Can't serialize the signature"); }
+    printf("Signature: ");
+    println_hex(der, len);
+
+    // verification
+    printf("=== Signature verification ===\r\n");
+    res = secp256k1_ecdsa_verify(ctx, &sig, hash, &pubkey);
+    if(res){
+        printf("Signature is valid\r\n");
+    }else{
+        printf("Invalid signature\r\n");
+    }
+
+    secp256k1_context_destroy(ctx);
+}
+
+int main(){
+    printf("Press any key to continue\r\n");
+    pc.getc();
+    printf("Ready to go!\r\n");
+
+    printf("=== Running example for secp256k1 ===\r\n");
+    secp_example();
+
+
+    printf("\r\n=== Done ===\r\n");
+
+}
\ No newline at end of file