1 files changed, 64 insertions, 0 deletions
diff --git a/crypto-mcf.c b/crypto-mcf.c
new file mode 100644
index 0000000..66e92f0
--- /dev/null
+++ b/crypto-mcf.c
@@ -0,0 +1,64 @@
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <float.h>
+
+#include <math.h>
+
+#include "libscrypt.h"
+
+/* Although log2 exists in GNU99 C, more portable code shouldn't use it
+* Note that this function returns a float and hence is not compatible with the
+* GNU prototype
+*/
+static double scrypt_log2( uint32_t n )  
+{  
+	// log(n)/log(2) is log2.  
+	double temp;
+	/* Using the temp variable keeps splint happy */
+	temp = log(2);
+	return (log((double)n) / temp);
+}
+
+int libscrypt_mcf(uint32_t N, uint32_t r, uint32_t p, char *salt, char *hash, char *mcf)
+{
+
+
+	uint32_t params;
+	int s;
+	double t, t2, fracpart;
+
+	if(!mcf || !hash)
+		return 0;
+	/* Although larger values of r, p are valid in scrypt, this mcf format
+	* limits to 8 bits. If your number is larger, current computers will
+	* struggle
+	*/
+	if(r > (uint8_t)(-1) || p > (uint8_t)(-1))
+		return 0;
+
+
+	t = scrypt_log2(N);
+
+	/* The "whole numebr" check below is non-trivial due to precision
+	* issues, where you could printf("%d", (int)t) and find yourself
+	* looking at (expected value) -1
+	*/
+	fracpart = modf(t, &t2);
+	if(fracpart > DBL_EPSILON)
+		return 0;
+		
+	params = (r << 8) + p;
+	params += (uint32_t)t << 16;
+	
+	/* Using snprintf - not checking for overflows. We've already
+	* determined that mcf should be defined as at least SCRYPT_MCF_LEN
+	* in length 
+	*/
+	s = snprintf(mcf, SCRYPT_MCF_LEN,  SCRYPT_MCF_ID "$%06x$%s$%s", (unsigned int)params, salt, hash);
+	if (s > SCRYPT_MCF_LEN)
+		return 0;
+
+	return 1;
+}