str 转 md5

 @interface NSString (MD5)

 + (NSString *)md5To32bit:(NSString *)str;

 @end

 @implementation NSString (MD5)

 + (NSString *)md5To32bit:(NSString *)str {

     const char *cStr = [str UTF8String];
     unsigned char digest[CC_MD5_DIGEST_LENGTH];
     CC_MD5( cStr, (CC_LONG)strlen(cStr),digest );
     NSMutableString *result = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * ];
     for(int i = ; i < CC_MD5_DIGEST_LENGTH; i++)
         [result appendFormat:@"%02x", digest[i]];
     return result;
 }

 @end