Java sha256与Swift sha256不匹配

Question

在Java和Swift中计算sha256时，它不匹配。

Java：

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]

Swift：

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，但随后开始不同

Answer 1

Bytes in Java are signed，因此它们只能表示-128到127的值，因此当它试图表示225 (第三个字节)时，它会溢出到-31。两个字节的实际二进制表示将是相同的1110 0001。