我正在尝试了解Java java.security.Signature 类的功能。如果我计算SHA1消息摘要，然后使用RSA加密该摘要，我会得到一个不同的结果，要求签名类签署相同的内容：
// Generate new key
KeyPair keyPair = KeyPairGenerator.getInstance("RSA").generateKeyPair();
PrivateKey privateKey = keyPair.getPrivate();
String plaintext = "This is the message being signed";
// Compute signature
Signature instance = Signature.getInstance("SHA1withRSA");
instance.initSign(privateKey);
instance.update((plaintext).getBytes());
byte[] signature = instance.sign();
// Compute digest
MessageDigest sha1 = MessageDigest.getInstance("SHA1");
byte[] digest = sha1.digest((plaintext).getBytes());
// Encrypt digest
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
byte[] cipherText = cipher.doFinal(digest);
// Display results
System.out.println("Input data: " + plaintext);
System.out.println("Digest: " + bytes2String(digest));
System.out.println("Cipher text: " + bytes2String(cipherText));
System.out.println("Signature: " + bytes2String(signature));
结果（例如）：
输入数据：这是正在签名的消息 摘要：62b0a9ef15461c82766fb5bdaae9edbe4ac2e067
密文：057dc0d2f7f54acc95d3cf5cba9f944619394711003bdd12 ...
签名：7177c74bbbb871cc0af92e30d2808ebae146f25d3fd8ba1622 ...
我必须对签名正在做什么有一个基本的误解 - 我已经跟踪了它，它似乎是在 MessageDigest 对象上调用update，如我所料，算法设置为SHA1，然后获取摘要，然后进行加密。是什么让结果有所不同？
修改
Leonidas让我检查签名方案是否应该按照我的想法行事。 RFC中定义了两种类型的签名：
first of these（PKCS1）是我上面描述的那个。它使用哈希函数创建摘要，然后使用私钥加密结果。
second algorithm使用随机盐值，更安全但不确定。如果重复使用相同的密钥，上面代码生成的签名不会改变，所以我不认为它可以是PSS。
修改
以下是我使用的bytes2string方法：
private static String bytes2String(byte[] bytes) {
StringBuilder string = new StringBuilder();
for (byte b : bytes) {
String hexString = Integer.toHexString(0x00FF & b);
string.append(hexString.length() == 1 ? "0" + hexString : hexString);
}
return string.toString();
}
答案 0 :(得分：51)
好的，我已经知道发生了什么。我当时很蠢。 Leonidas是对的，它不仅仅是加密的哈希值，而是与摘要连接的哈希算法的ID：
DigestInfo ::= SEQUENCE {
digestAlgorithm AlgorithmIdentifier,
digest OCTET STRING
}
这就是他们与众不同的原因。
答案 1 :(得分：9)
产生相同的结果：
MessageDigest sha1 = MessageDigest.getInstance("SHA1", BOUNCY_CASTLE_PROVIDER);
byte[] digest = sha1.digest(content);
DERObjectIdentifier sha1oid_ = new DERObjectIdentifier("1.3.14.3.2.26");
AlgorithmIdentifier sha1aid_ = new AlgorithmIdentifier(sha1oid_, null);
DigestInfo di = new DigestInfo(sha1aid_, digest);
byte[] plainSig = di.getDEREncoded();
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", BOUNCY_CASTLE_PROVIDER);
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
byte[] signature = cipher.doFinal(plainSig);
答案 2 :(得分：4)
答案 3 :(得分：4)
一个稍高效的bytes2String方法版本是
private static final char[] hex = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
private static String byteArray2Hex(byte[] bytes) {
StringBuilder sb = new StringBuilder(bytes.length * 2);
for (final byte b : bytes) {
sb.append(hex[(b & 0xF0) >> 4]);
sb.append(hex[b & 0x0F]);
}
return sb.toString();
}
答案 4 :(得分：1)
将@Mike Houston的答案作为指针，这是一个完整的示例代码，可以执行签名和哈希以及加密。
/**
* @param args
*/
public static void main(String[] args)
{
try
{
boolean useBouncyCastleProvider = false;
Provider provider = null;
if (useBouncyCastleProvider)
{
provider = new BouncyCastleProvider();
Security.addProvider(provider);
}
String plainText = "This is a plain text!!";
// KeyPair
KeyPairGenerator keyPairGenerator = null;
if (null != provider)
keyPairGenerator = KeyPairGenerator.getInstance("RSA", provider);
else
keyPairGenerator = KeyPairGenerator.getInstance("RSA");
keyPairGenerator.initialize(2048);
KeyPair keyPair = keyPairGenerator.generateKeyPair();
// Signature
Signature signatureProvider = null;
if (null != provider)
signatureProvider = Signature.getInstance("SHA256WithRSA", provider);
else
signatureProvider = Signature.getInstance("SHA256WithRSA");
signatureProvider.initSign(keyPair.getPrivate());
signatureProvider.update(plainText.getBytes());
byte[] signature = signatureProvider.sign();
System.out.println("Signature Output : ");
System.out.println("\t" + new String(Base64.encode(signature)));
// Message Digest
String hashingAlgorithm = "SHA-256";
MessageDigest messageDigestProvider = null;
if (null != provider)
messageDigestProvider = MessageDigest.getInstance(hashingAlgorithm, provider);
else
messageDigestProvider = MessageDigest.getInstance(hashingAlgorithm);
messageDigestProvider.update(plainText.getBytes());
byte[] hash = messageDigestProvider.digest();
DigestAlgorithmIdentifierFinder hashAlgorithmFinder = new DefaultDigestAlgorithmIdentifierFinder();
AlgorithmIdentifier hashingAlgorithmIdentifier = hashAlgorithmFinder.find(hashingAlgorithm);
DigestInfo digestInfo = new DigestInfo(hashingAlgorithmIdentifier, hash);
byte[] hashToEncrypt = digestInfo.getEncoded();
// Crypto
// You could also use "RSA/ECB/PKCS1Padding" for both the BC and SUN Providers.
Cipher encCipher = null;
if (null != provider)
encCipher = Cipher.getInstance("RSA/NONE/PKCS1Padding", provider);
else
encCipher = Cipher.getInstance("RSA");
encCipher.init(Cipher.ENCRYPT_MODE, keyPair.getPrivate());
byte[] encrypted = encCipher.doFinal(hashToEncrypt);
System.out.println("Hash and Encryption Output : ");
System.out.println("\t" + new String(Base64.encode(encrypted)));
}
catch (Throwable e)
{
e.printStackTrace();
}
}
您可以使用BouncyCastle Provider或默认的Sun Provider。
答案 5 :(得分：0)
我有类似的问题，我测试了添加代码并发现了一些有趣的结果。 我添加了这个代码，我可以推断，根据要使用的“提供者”，公司可以有所不同吗？ （因为加密中包含的数据在所有提供者中并不总是相同的。）
Conclusion.- 签名解密= ???（垃圾）+ DigestInfo（如果我们知道“垃圾”的值，数字签名将是相等的）
输入数据：这是正在签名的消息
摘要：62b0a9ef15461c82766fb5bdaae9edbe4ac2e067
DigestInfo：3021300906052b0e03021a0500041462b0a9ef15461c82766fb5bdaae9edbe4ac2e067
签名破译：1ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff003021300906052b0e03021a0500041462b0a9ef15461c82766fb5bdaae9edbe4ac2e067
import java.security.InvalidKeyException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.SignatureException;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import org.bouncycastle.asn1.x509.DigestInfo;
import org.bouncycastle.asn1.DERObjectIdentifier;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
public class prueba {
/**
* @param args
* @throws NoSuchProviderException
* @throws NoSuchAlgorithmException
* @throws InvalidKeyException
* @throws SignatureException
* @throws NoSuchPaddingException
* @throws BadPaddingException
* @throws IllegalBlockSizeException
*///
public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchProviderException, InvalidKeyException, SignatureException, NoSuchPaddingException, IllegalBlockSizeException, BadPaddingException {
// TODO Auto-generated method stub
KeyPair keyPair = KeyPairGenerator.getInstance("RSA","BC").generateKeyPair();
PrivateKey privateKey = keyPair.getPrivate();
PublicKey puKey = keyPair.getPublic();
String plaintext = "This is the message being signed";
// Hacer la firma
Signature instance = Signature.getInstance("SHA1withRSA","BC");
instance.initSign(privateKey);
instance.update((plaintext).getBytes());
byte[] signature = instance.sign();
// En dos partes primero hago un Hash
MessageDigest digest = MessageDigest.getInstance("SHA1", "BC");
byte[] hash = digest.digest((plaintext).getBytes());
// El digest es identico a openssl dgst -sha1 texto.txt
//MessageDigest sha1 = MessageDigest.getInstance("SHA1","BC");
//byte[] digest = sha1.digest((plaintext).getBytes());
AlgorithmIdentifier digestAlgorithm = new AlgorithmIdentifier(new
DERObjectIdentifier("1.3.14.3.2.26"), null);
// create the digest info
DigestInfo di = new DigestInfo(digestAlgorithm, hash);
byte[] digestInfo = di.getDEREncoded();
//Luego cifro el hash
Cipher cipher = Cipher.getInstance("RSA","BC");
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
byte[] cipherText = cipher.doFinal(digestInfo);
//byte[] cipherText = cipher.doFinal(digest2);
Cipher cipher2 = Cipher.getInstance("RSA","BC");
cipher2.init(Cipher.DECRYPT_MODE, puKey);
byte[] cipherText2 = cipher2.doFinal(signature);
System.out.println("Input data: " + plaintext);
System.out.println("Digest: " + bytes2String(hash));
System.out.println("Signature: " + bytes2String(signature));
System.out.println("Signature2: " + bytes2String(cipherText));
System.out.println("DigestInfo: " + bytes2String(digestInfo));
System.out.println("Signature Decipher: " + bytes2String(cipherText2));
}
答案 6 :(得分：0)
下面的代码（取自我的博客文章 - http://todayguesswhat.blogspot.com/2021/01/manually-verifying-rsa-sha-signature-in.html）希望有助于理解带有 RSA 签名的标准 SHA 中存在的内容。这应该适用于标准 Oracle JDK，不需要 Bouncy Castle 库。它使用 sun.security 类来处理解密的签名内容 - 您可以轻松地手动解析。
在下面的示例中，消息摘要算法是 SHA-512，它生成 64 字节（512 位）校验和。
SHA-1 非常相似 - 但会生成 20 字节（160 位）校验和。
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.MessageDigest;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.util.Arrays;
import javax.crypto.Cipher;
import sun.security.util.DerInputStream;
import sun.security.util.DerValue;
public class RSASignatureVerification
{
public static void main(String[] args) throws Exception
{
KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
generator.initialize(2048);
KeyPair keyPair = generator.generateKeyPair();
PrivateKey privateKey = keyPair.getPrivate();
PublicKey publicKey = keyPair.getPublic();
String data = "hello oracle";
byte[] dataBytes = data.getBytes("UTF8");
Signature signer = Signature.getInstance("SHA512withRSA");
signer.initSign(privateKey);
signer.update(dataBytes);
byte[] signature = signer.sign(); // signature bytes of the signing operation's result.
Signature verifier = Signature.getInstance("SHA512withRSA");
verifier.initVerify(publicKey);
verifier.update(dataBytes);
boolean verified = verifier.verify(signature);
if (verified)
{
System.out.println("Signature verified!");
}
/*
The statement that describes signing to be equivalent to RSA encrypting the
hash of the message using the private key is a greatly simplified view
The decrypted signatures bytes likely convey a structure (ASN.1) encoded
using DER with the hash just one component of the structure.
*/
// lets try decrypt signature and see what is in it ...
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, publicKey);
byte[] decryptedSignatureBytes = cipher.doFinal(signature);
/*
sample value of decrypted signature which was 83 bytes long
30 51 30 0D 06 09 60 86 48 01 65 03 04 02 03 05
00 04 40 51 00 41 75 CA 3B 2B 6B C0 0A 3F 99 E3
6B 7A 01 DC F2 9B 36 E6 0D D4 31 89 53 A3 D9 80
6D AE DD 45 7E 55 45 01 FC C8 73 D2 DD 8D E5 B9
E0 71 57 13 41 D0 CD FF CA 58 01 03 A3 DD 95 A1
C1 EE C8
Taking above sample bytes ...
0x30 means A SEQUENCE - which contains an ordered field of one or more types.
It is encoded into a TLV triplet that begins with a Tag byte of 0x30.
DER uses T,L,V (tag bytes, length bytes, value bytes) format
0x51 is the length = 81 decimal (13 bytes)
the 0x30 (48 decimal) that follows begins a second sequence
https://tools.ietf.org/html/rfc3447#page-43
the DER encoding T of the DigestInfo value is equal to the following for SHA-512
0D 06 09 60 86 48 01 65 03 04 02 03 05 00 04 40 || H
where || is concatenation and H is the hash value.
0x0D is the length = 13 decimal (13 bytes)
0x06 means an OBJECT_ID tag
0x09 means the object id is 9 bytes ...
https://docs.microsoft.com/en-au/windows/win32/seccertenroll/about-object-identifier?redirectedfrom=MSDN
taking 2.16.840.1.101.3.4.2.3 (object id for SHA512 Hash Algorithm)
The first two nodes of the OID are encoded onto a single byte.
The first node is multiplied by the decimal 40 and the result is added to the value of the second node
2 * 40 + 16 = 96 decimal = 60 hex
Node values less than or equal to 127 are encoded on one byte.
1 101 3 4 2 3 corresponds to in hex 01 65 03 04 02 03
Node values greater than or equal to 128 are encoded on multiple bytes.
Bit 7 of the leftmost byte is set to one. Bits 0 through 6 of each byte contains the encoded value.
840 decimal = 348 hex
-> 0000 0011 0100 1000
set bit 7 of the left most byte to 1, ignore bit 7 of the right most byte,
shifting right nibble of leftmost byte to the left by 1 bit
-> 1000 0110 X100 1000 in hex 86 48
05 00 ; NULL (0 Bytes)
04 40 ; OCTET STRING (0x40 Bytes = 64 bytes
SHA512 produces a 512-bit (64-byte) hash value
51 00 41 ... C1 EE C8 is the 64 byte hash value
*/
// parse DER encoded data
DerInputStream derReader = new DerInputStream(decryptedSignatureBytes);
byte[] hashValueFromSignature = null;
// obtain sequence of entities
DerValue[] seq = derReader.getSequence(0);
for (DerValue v : seq)
{
if (v.getTag() == 4)
{
hashValueFromSignature = v.getOctetString(); // SHA-512 checksum extracted from decrypted signature bytes
}
}
MessageDigest md = MessageDigest.getInstance("SHA-512");
md.update(dataBytes);
byte[] hashValueCalculated = md.digest();
boolean manuallyVerified = Arrays.equals(hashValueFromSignature, hashValueCalculated);
if (manuallyVerified)
{
System.out.println("Signature manually verified!");
}
else
{
System.out.println("Signature could NOT be manually verified!");
}
}
}