iOS的文件校验码生成 - ObjC编写

一般我们比较文件的完整性，就是对文件进行哈希计算，通常就是MD5或者SHA256或者SHA1计算，如果生成的结果字符串是一样的，则表明文件没有被篡改

比如我们在网络上下载的安装包，下载时都会提示MD5或者SHA1的校验码是多少？有没有想过校验码是如何生成的了？以下就是用Objective-C来对文件计算checksum即校验码是否 服务器端存储的一致，如果是一致的，则表示文件是完整的

#import "FileChecksumUtil.h"
#import <CommonCrypto/CommonDigest.h>

@implementation FileChecksumUtil

// MD5 hash for file 对文件进行MD5 HASH计算
+ (NSString * _Nullable)md5HashForFileWithFullPath:(NSString *)fullPath {
    NSFileManager *fileManager = [NSFileManager defaultManager];
    // Make sure the file exists
    if( [fileManager fileExistsAtPath:fullPath isDirectory:nil]) {
        NSData *data = [NSData dataWithContentsOfFile:fullPath];
        unsigned char digest[CC_MD5_DIGEST_LENGTH];
        CC_MD5(data.bytes, (CC_LONG)data.length, digest);
 
        NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
        for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) {
            [output appendFormat:@"%02x", digest[i]];
        }
        return output;
    }
    return nil;
}

// 对文件进行SHA256 HASH计算
+ (NSString * _Nullable)sha256HashForFileWithFullPath:(NSString *)fullPath {
    NSFileManager *fileManager = [NSFileManager defaultManager];
    // Make sure the file exists
    if( [fileManager fileExistsAtPath:fullPath isDirectory:nil] ) {
        NSData *data = [NSData dataWithContentsOfFile:fullPath];
        unsigned char digest[CC_SHA256_DIGEST_LENGTH];
        CC_SHA256(data.bytes, (CC_LONG)data.length, digest);
 
        NSMutableString *output = [NSMutableString stringWithCapacity:CC_SHA256_DIGEST_LENGTH * 2];
 
        for (int i = 0; i < CC_SHA256_DIGEST_LENGTH; i++) {
            [output appendFormat:@"%02x", digest[i]];
        }
        return output;
    }
    return nil;
}

@end


// 测试
NSString *fullPath = @"/Users/victorzhang/Documents/20200730-资料.zip"; 
NSString *md5 = [FileChecksumUtil md5HashForFileWithFullPath:fullPath];
NSString *sha1 = [FileChecksumUtil sha256HashForFileWithFullPath:fullPath];
     
NSLog(@"MD5: %@", md5);
NSLog(@"SHA256: %@", sha1);

输出

MD5: db620a4c2f33899dfea298fb8377938b
SHA256: f6b77493ce07b40b25c6c2789284d92a7d23e0d68b95df766f1f2144f4fae6ad