iOS SHA1算法

以下是常量：
#define CC_SHA1_DIGEST_LENGTH 20
#define kMChosenDigestLength CC_SHA1_DIGEST_LENGTH
//哈希算法

+ (NSData *)getHashBytes:(NSData *)plaintText {    CC_SHA1_CTX ctx;    uint8_t *hashBytes = NULL;    NSData *hash = nil;    // Malloc a buffer to hold hash    hashBytes = malloc(kMChosenDigestLength * sizeof(uint8_t));    memset((void *)hashBytes, 0x0, kMChosenDigestLength);    // Initialize the context.    CC_SHA1_Init(&ctx);    // Perform the hash.    CC_SHA1_Update(&ctx, (void *)[plaintText bytes], (uint32_t)[plaintText length]);    // Finalize the out put.    CC_SHA1_Final(hashBytes, &ctx);    // Build up the SHA1 hash.    hash = [NSData dataWithBytes:(const void *)hashBytes length:(NSUInteger)kMChosenDigestLength];    if (hashBytes) free(hashBytes);    return hash;}