Some example code for generating an EC keypair and using it to sign some data using the ECDSA algorithm.

#include <multos.h>

#define HASH_LEN 32
#define PRIME_LEN 32

// Structures for keys
typedef struct
{
	BYTE x[PRIME_LEN];
	BYTE y[PRIME_LEN];
} ecc_public_s;

typedef struct
{
	ecc_public_s publicKey;
	BYTE privateKey[PRIME_LEN];
} ecc_s;

typedef struct
{
	BYTE r[PRIME_LEN];
	BYTE s[PRIME_LEN];
} ecc_sig_s;

#pragma melstatic
BYTE domainParams[] = {		// SECP256K1
 0x00 , // Format
 0x20 , // Prime length
 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F, //P
 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, //A
 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x07, //B
 0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,0x0B,0x07,
 0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,0x17,0x98, // Gx
 0x48,0x3A,0xDA,0x77,0x26,0xA3,0xC4,0x65,0x5D,0xA4,0xFB,0xFC,0x0E,0x11,0x08,0xA8,
 0xFD,0x17,0xB4,0x48,0xA6,0x85,0x54,0x19,0x9C,0x47,0xD0,0x8F,0xFB,0x10,0xD4,0xB8, // Gy
 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFE,
 0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,0x8C,0xD0,0x36,0x41,0x41, // N
 0x01  // H
};
ecc_s eccKeyPair;

#pragma melsession	
ecc_sig_s signature;
BYTE hash[HASH_LEN];
	
	// .. in code
	// Generate key pair
	genOK = multosEccGenerateKeyPair((BYTE*)&eccKeyPair,domainParams);

	if(genOK)
	{
		// Hash the data to be signed
		multosSecureHash((BYTE*)&data,hash,sizeof(hash),sizeof(data));

		// Sign the hash
		genOK = multosECDSA((BYTE*)&signature,hash+(HASH_LEN-PRIME_LEN),eccKeyPair.privateKey,domainParams);
		if(genOK)
		{
			// Verify the signature
			if(multosECDSAVerify(hash,(BYTE*)&signature,(BYTE*)&eccKeyPair.publicKey,domainParams))
				multosExitSW(0x9000);	// OK
			else
				multosExitSW(0x9001);
		}
		else
			multosExitSW(0x9002);
	}
	else
		multosExitSW(0x9001);