如何在ios中生成SHA256和CRC32

Question

我正在做一个文件上传工作。我想生成 SHA256 和 CRC32 哈希。谁能帮助我如何生成这些哈希？我想让它适用于 iOS。

Answer 1

SHA256 在 CommonCrypto 中可用。 CRC32 不是哈希，它是循环冗余校验。

示例代码：

#import <CommonCrypto/CommonDigest.h>

NSData *dataIn = [@"Now is the time for all good computers to come to the aid of their masters." dataUsingEncoding:NSASCIIStringEncoding];
NSMutableData *macOut = [NSMutableData dataWithLength:CC_SHA256_DIGEST_LENGTH];

CC_SHA256(dataIn.bytes, dataIn.length,  macOut.mutableBytes);

NSLog(@"dataIn: %@", dataIn);
NSLog(@"macOut: %@", macOut);

NSLog 输出：
dataIn:

macOut:

Answer 2

对于这两个，您可以使用以下要点：

https://gist.github.com/paul-delange/6808278

还有一个例子

NSString* crc32 = (__bridge NSString*)TGDFileHashCreateWithPath((__bridge CFStringRef)filepath, TGDFileHashDefaultChunkSizeForReadingData, TGDChecksumAlgorithmCRC32);

Answer 3

此方法将从文件路径生成 iOS 上 gcloud 使用的 crc32c。如果您想要标准 crc32，只需取消注释 CRC32_POLYNOMIAL 的其他值。

它读取 512KB 块中给定的文件，因此可以用于大文件。

- (NSString*) crc32c:(NSString*)filepath{

    ///  using crc code from
    //   http://classroomm.com/objective-c/index.php?action=printpage;topic=2891.0
    //   by rgronlie


    //this is the standard crc32 polynomial
    //uint32_t CRC32_POLYNOMIAL = 0xEDB88320;

    //this is the crc32c one
    uint32_t CRC32_POLYNOMIAL = 0x82F63B78L;
    uint32_t  CRC32C_SEED = 0xFFFFFFFFL;

    // create and populate a lookup table
    uint32_t* pCRCTable = malloc(sizeof(uint32_t) * 256);

    for (uint32_t i = 0; i <= 255; i++)
    {
        uint32_t crc32 = i;
        for (uint32_t j = 8; j > 0; j--)
        {
            if ((crc32 & 1) == 1)
                crc32 = (crc32 >> 1) ^ CRC32_POLYNOMIAL;
            else
                crc32 >>= 1;
        }
        pCRCTable[i] = crc32;
    }

    // get a handle to the file
    NSFileHandle *filehandle = [NSFileHandle fileHandleForReadingAtPath:filepath];

    if(filehandle == NULL){
        NSLog(@"failed to create file handle");
        return nil;
    }

    // a buffer to read into
    NSData* databuffer;

    uint32_t crc = CRC32C_SEED;

    // read the file in chunks of 512KB

    while(true){
        databuffer = [filehandle readDataOfLength: 512 * 1024];

        // if there is nothing left finish
        if([databuffer length] == 0){
            break;
        }
        // otherwise run each chunk through the lookup table
        uint8_t *pBytes = (uint8_t *)[databuffer bytes];
        uint32_t length = [databuffer length];

        while (length--)
        {
            crc = (crc>>8) ^ pCRCTable[(crc & 0xFF) ^ *pBytes++];
        }
    }

    // clean up
    [filehandle closeFile];
    free(pCRCTable);

    // this is the result
    uint32_t hash = crc ^ 0xFFFFFFFFL;

    // reverse it for endianness
    uint32_t hash_reversed = CFSwapInt32HostToBig(hash);
    // as raw bytes
    NSData* hash_data = [NSData dataWithBytes: &hash_reversed length: sizeof(hash_reversed)];
    // return base64 encoded
    return [hash_data base64EncodedStringWithOptions:0];
}

Answer 4

没有可以为 ios 生成哈希的应用

这应该可以工作....它适用于 Mac

http://itunes.apple.com/us/app/digiprint/id473233587?mt=12