Move system dependency on /dev/urandom out of totp.c

Author: kmeow

totp.c

@@ -101,7 +101,7 @@ static time_t flip_ts_endianness(time_t timestamp)
 	return output;
 }
 
-int generate_random_secret(char* out, size_t outlen)
+int generate_random_secret(char* out, size_t outlen, int32_t (*rgen)(uint8_t*, size_t))
 {
 	//Generate a 160-bit random value encoded in a 32 character long base32
 	//encoded ASCII string
@@ -112,16 +112,7 @@ int generate_random_secret(char* out, size_t outlen)
 
 	uint8_t secret[20] = {0};
 
-	FILE* fpurandom = fopen("/dev/urandom", "r");
-	if(!fpurandom)
-	{
-		return -1;
-	}
-
-	int bread = fread(secret, 1, 20, fpurandom);
-	fclose(fpurandom);
-
-	if(bread < 20)
+	if(rgen(secret, 20) < 0)
 	{
 		return -1;
 	}

totp.h

@@ -60,12 +60,13 @@ int32_t compute_totp(const char* secret, size_t secretlen,
  * timestep - how many seconds OTP should remain valid; almost always 30
  * digits - how many digits (1 - 8) should be in the OTP. 6 is common
  */
-
-int generate_random_secret(char* out, size_t outlen);
+int generate_random_secret(char* out, size_t outlen, int32_t (*rgen)(uint8_t*, size_t));
 /* generate_random_secret: generates a random secret encoded in base32.
  *
  * out - pointer to output buffer
  * outlen - size of buffer in bytes. Must be at least 33 bytes long.
+ * rgen - a function that fills the buffer pointed to by the first argument, of length equal to the 2nd argument, with random bytes
+ *	  and which returns -1 on failure and anything else on success
  */
 
  void hmacsha1(char* output, const char* key,

totp_demo.c

@@ -25,11 +25,25 @@
 #include "totp.h"
 #include "base32codec.h"
 
+int32_t FillFromURANDOM(uint8_t* out, size_t outlen)
+{
+	FILE* fpurandom = fopen("/dev/urandom", "r");
+	if(!fpurandom)
+	{
+		return -1;
+	}
+
+	int32_t bread = fread(out, 1, outlen, fpurandom);
+	fclose(fpurandom);
+
+	return bread < outlen ? -1 : bread;
+}
+
 void demo_ansi_qrcode()
 {
 	char secret[33] = {0};
 	//Create a base32 encoded secret in an ascii string
-	generate_random_secret(secret, 33);
+	generate_random_secret(secret, 33, FillFromURANDOM);
 	printf("Secret: %s\n", secret);
 
 	//Create an ANSI QR code graphic. qrcodeansi owns the new heap memory.