不同的加密在Android和纯Java中 – RSA/ECB/OAEPWithMD5AndMGF1Padding

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英文:

Different encryption Android vs pure Java - RSA/ECB/OAEPWithMD5AndMGF1Padding

问题

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英文:

I encrypt a string in Android by the public key. However, I get an exception "Decryption error" when I try to decrypt the encrypted string by the private key in pure Java code. Can anyone help to find the problem?

Android code to encrypt

import android.util.Base64;
public static String encryptMessage(final String plainText, final PublicKey publicKey) throws Exception {
    Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithAndMGF1Padding");
    cipher.init(Cipher.ENCRYPT_MODE, publicKey);
    return Base64.encodeToString(cipher.doFinal(plainText.getBytes()), Base64.NO_WRAP);
}

Pure Java code to decrypt

import java.util.Base64;
public static String decryptMessage(final String encryptedText, final PrivateKey privateKey) throws Exception {
    Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithAndMGF1Padding");
    cipher.init(Cipher.DECRYPT_MODE, privateKey);

    Base64.Decoder decoder = Base64.getDecoder();
    byte[] byteArray = decoder.decode(encryptedText);
    byte[] decryptedArray = cipher.doFinal(byteArray);  // throw exception here
    String plainText = new String(decryptedArray);
    return plainText;
}

You may notice I have to use different Base64 APIs in Android and pure Java. I tried "RSA/ECB/PKCS1Padding", and it can decrypt correctly without the exception. Tried "RSA/ECB/OAEPWithSHA-256AndMGF1Padding" too but got the same exception.

答案1

得分: 5

OAEP使用两个摘要,一个用于OAEP标签,第二个作为MGF1的基础,详见RFC 8017,7.1. RSAES-OAEPB.1. 哈希函数B.2. 掩码生成函数

问题是由于在OP代码(Android / API Level 28和Java 8)的两侧使用的提供程序对于OAEPWithMD5AndMGF1Padding应用了不同的MGF1摘要。

在两侧,相关参数(提供程序、OAEP摘要、MGF、MGF1摘要)可以在密码器初始化后确定,例如:

OAEPParameterSpec parameterSpec = cipher.getParameters().getParameterSpec(OAEPParameterSpec.class);
System.out.println("Provider: " + cipher.getProvider().getName());          
System.out.println("OAEP digest: " + parameterSpec.getDigestAlgorithm());  
System.out.println("OAEP MGF : " + parameterSpec.getMGFAlgorithm());        
System.out.println("OAEP MGF1 digest: " + ((MGF1ParameterSpec)parameterSpec.getMGFParameters()).getDigestAlgorithm()); 

通过这种方式,在Android端确定MD5被确定为MGF1摘要,在Java端确定为SHA-1。在两侧,MD5被用作OAEP摘要。如果使用OAEPParameterSpec显式设置摘要,问题可以得以解决,以便在两侧使用相同的摘要。

例如,以下Java端的代码确保MD5被用作OAEP和MGF1摘要,类似于Android端:

OAEPParameterSpec oaepParameterSpecDec = new OAEPParameterSpec("MD5", "MGF1", new MGF1ParameterSpec("MD5"), PSource.PSpecified.DEFAULT);
cipher.init(Cipher.DECRYPT_MODE, privateKey, oaepParameterSpecDec);

对于OAEPWithSHA-256AndMGF1Padding也是一样的。

还要注意,RFC 8017在B.1. 哈希函数中推荐为RSAES-OAEP使用SHA-1和SHA-2,但推荐使用MD5。

英文:

OAEP uses two digests, one for the OAEP label and a second as the basis for MGF1, see RFC 8017, 7.1. RSAES-OAEP, B.1. Hash Functions and B.2. Mask Generation Functions.

The issue is caused because the providers used on both sides of the OP code (Android / API Level 28 and Java 8) apply different MGF1 digests for OAEPWithMD5AndMGF1Padding.

On both sides the relevant parameters (provider, OAEP digest, MGF, MGF1 digest) can be determined after the initialization of the cipher e.g. with:

OAEPParameterSpec parameterSpec = cipher.getParameters().getParameterSpec(OAEPParameterSpec.class);
System.out.println("Provider: " + cipher.getProvider().getName());          
System.out.println("OAEP digest: " + parameterSpec.getDigestAlgorithm());  
System.out.println("OAEP MGF : " + parameterSpec.getMGFAlgorithm());        
System.out.println("OAEP MGF1 digest: " + ((MGF1ParameterSpec)parameterSpec.getMGFParameters()).getDigestAlgorithm()); 

With this, MD5 is determined as MGF1 digest on the Android side and SHA-1 on the Java side. On both sides MD5 is used as OAEP digest. The issue can be fixed if the digests are explicitly set with OAEPParameterSpec so that the same digests are used on both sides.

For example, the following code on the Java side ensures that MD5 is used as OAEP and MGF1 digest, analogous to the Android side.

OAEPParameterSpec oaepParameterSpecDec = new OAEPParameterSpec("MD5", "MGF1", new MGF1ParameterSpec("MD5"), PSource.PSpecified.DEFAULT);
cipher.init(Cipher.DECRYPT_MODE, privateKey, oaepParameterSpecDec);

The same applies to OAEPWithSHA-256AndMGF1Padding.

Note also that RFC 8017 in B.1. Hash Functions recommends SHA-1 and SHA-2 for RSAES-OAEP, but not MD5.

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  • 本文由 发表于 2020年5月30日 15:10:39
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