Java sha256与Swift sha256不匹配

Question

在Java和Swift中计算sha256时,它不匹配.

Java的:

MessageDigest digest = MessageDigest.getInstance("SHA-256");
digest.update(secretKey.getBytes("UTF-8"));

byte[] secretKeyBytes = secretKey.getBytes("UTF-8");

byte[] keyBytes = new byte[16];
System.arraycopy(digest.digest(), 0, keyBytes, 0, keyBytes.length);

结果: [44, 112, -31, 43, 122, 6, 70, -7, 34, 121, -12, 39, -57, -77, -114, 115]

迅速:

let secretKeyBytes = [UInt8](secretKey.utf8)

var digest = SHA2(variant: SHA2.Variant.sha256)
try digest.update(withBytes: secretKeyBytes)
let keyDigest = try digest.finish()

let keyBytes = Array(keyDigest[0...15])

结果: [44, 112, 225, 43, 122, 6, 70, 249, 34, 121, 244, 39, 199, 179, 142, 115]

它以相同的值开始,但随后开始变化

Answer 1

Java中的字节是有符号的,因此它们只能表示-128到127的值,因此当它尝试表示溢出到-31的225(第三个字节)时.两个字节的实际二进制表示将是相同的1110 0001.