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Getting java.lang.ArrayIndexOutOfBoundsException error: too much data for RSA block

I have a private pem key file, I use this file to sign and encrypt data. Signing works fine, and I can also check on a different platform, but when encrypting the data, I get the following error:

04-04 09:55:51.821: E/AndroidRuntime(2725): FATAL EXCEPTION: Thread-102 04-04 09:55:51.821: E/AndroidRuntime(2725): java.lang.ArrayIndexOutOfBoundsException: too much data for RSA block 04-04 09:55:51.821: E/AndroidRuntime(2725): at com.android.org.bouncycastle.jce.provider.JCERSACipher.engineDoFinal(JCERSACipher.java:457) 04-04 09:55:51.821: E/AndroidRuntime(2725): at javax.crypto.Cipher.doFinal(Cipher.java:1106) 04-04 09:55:51.821: E/AndroidRuntime(2725): at com.example.testsigning.MainActivity.rsaEncrypt(MainActivity.java:185) 04-04 09:55:51.821: E/AndroidRuntime(2725): at com.example.testsigning.MainActivity$1.run(MainActivity.java:51) 04-04 09:55:51.821: E/AndroidRuntime(2725): at java.lang.Thread.run(Thread.java:856)

The following is a snippet of code for extracting keys from a private file:

 // Read the file into string String privKeyPEM = readFile("/mnt/sdcard/rsa_key"); privKeyPEM = privKeyPEM.replace("-----BEGIN RSA PRIVATE KEY-----", ""); privKeyPEM = privKeyPEM.replace("-----END RSA PRIVATE KEY-----", ""); // Base64 decode the data byte[] encoded = Base64.decode(privKeyPEM, Base64.DEFAULT); // PKCS8 decode the encoded RSA private key PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded); KeyFactory kf = KeyFactory.getInstance("RSA"); mPrivKey = kf.generatePrivate(keySpec); RSAPrivateCrtKey privk = (RSAPrivateCrtKey) mPrivKey; RSAPublicKeySpec pubKeySpec = new java.security.spec.RSAPublicKeySpec( privk.getPublicExponent(), privk.getModulus()); mPubKey = kf.generatePublic(pubKeySpec);

The following is a code snippet for data encryption:

 Cipher cipher = Cipher.getInstance("RSA/None/OAEPWithSHA1AndMGF1Padding", "BC"); cipher.init(Cipher.ENCRYPT_MODE, mPubKey); return cipher.doFinal("Hello World".getBytes()); // here is the problem

Any help to solve the problem would be greatly appreciated.

Regards, Yuvi

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3 answers

The problem was extracting the public key from the private key, it should look like this:

 RSAPublicKeySpec pubKeySpec = new java.security.spec.RSAPublicKeySpec( privk.getModulus(), privk.getPublicExponent());

instead:

 RSAPublicKeySpec pubKeySpec = new java.security.spec.RSAPublicKeySpec( privk.getPublicExponent(), privk.getModulus());
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This error message occurs when the input buffer is larger than the size of the encryption input block. It seems unlikely that this will be the case with a short input line, so the first thing to look at is the previous line. I think the cipher is not initialized properly, or rather, not as you expect, as it does not throw an exception. I would start by debugging the encryption object after calling init() .

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Damn, I had the same error, but the reason was that I was reading decryption material using StringBuilder instead of ByteArrayOutputStream (the StringBuilder instance uses the append method, which adds the string and damages the source source for decryption).

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