Noticed this in the Facebook Connect source code. Looks pretty solid, give it a shot.
#import
...
+ (NSString*)md5HexDigest:(NSString*)input {
const char* str = [input UTF8String];
unsigned char result[CC_MD5_DIGEST_LENGTH];
CC_MD5(str, strlen(str), result);
NSMutableString *ret = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH*2];
for(int i = 0; i
