RSA decryption with 2048 bit key is giving bad data for encrypted text of length 340 on windows server 2012 r2,while it is working fine on windows 8

Question

  RSACryptoServiceProvider objRsaCrypto= new RSACryptoServiceProvider();
string xmlString = "<RSAKeyValue><Modulus>vafMwhQ1Z+zx1tpcUybDONf3M7IG8Xw6Q0eCsuWMRniqwUklnzndo9ExuAFC87oAywOcSSzSncLEgILxjiyNmnBe28whdDg+P1PJmDchmBIjzQKNpDIppOiaxGOUR8KqBwIMp24dZQtUqb9mElEEz5bOxZUwHLg2/fJ9bT+eE+VluHtYfuuS/nbhrvI6BHN2bm2CyITBAvT6loCm7mV/JZ0fT9nCsyn6rUsp+YCVbhrfMnyz9aW7NEkwncE7xz78LSIHaYgB19nPu5jkR6yUCLsNDV9wnOBjb1Xuh7NqTjt2yOAcH+Gt5ixukfKBROq67FlnQKZOa+mQNzkhytEeyw==</Modulus><Exponent>AQAB</Exponent><P>4tDAYRgWNcyB5dCN7kF8QUa4ddiw6siEblGnjcFpdrQLyJxFvCZ7Jlc/59Wmr8B/1G06coRla5NLBCtvh/Itovacfp00wNif5pBb/Tp9+quw5/GGSu/4/K/Ke0wQuhHdWNjzAriNxbpCRWD/EgzNngWS8KlufdymZyju6AWyEZk=</P><Q>1g8B7fQ3SMDZ2EyaiSscchj3lshJx9VR8EAN70aipu45LRsOWuHH7wTkfqp1LuB06LyCr7XLMwUQYrBM8mJOhtxsiissXe+Phw1kcXJo6hBrCPgfSKSkuHT8iR7OgZbzYA8zwMmr+m2WOuDsgxrQcb+hRVdC1QODqFb8C08YegM=</Q><DP>vW5Zbf4e9pmx142CLH3219HH12y9/aiwqi56QPNLML+Yo9iYiVaePdxa3DZdO6YLXRBI40HeLqVa3sWkJadHJDbRZxHG8FU73uWsXmcOtl/UpTLb1RRtICV1d9qEkdK/yiePdjNK/Nvd43HqNloJFLRVD7iCNo4lUD0ooxG2sek=</DP><DQ>BCeWaf/rcsYLdF9IQJFNpAlIBO0uQWqqhHc5zgMY9RR6l52G0czADKuTo8G7NIW2vy2pe6+TmhHnF4NEew/dZlCw6p2b5tbXek+QO4N09dYLvcjTEp3fdJUQsbifWXSMlLi20G8Zn2qxF8N107WZhhuqDaZ77ZZ737CQg8etOfE=</DQ><InverseQ>xEjq9mm61gofysxxgM6SnX5TQ5Lnpq0AvnsRBhQaatiGm8i+VnznMpk8zJgn/AspaYS62bFC/UdCd/b2VyXgZfBC/L1NdkIUNyOVAxNKhf95C4uQFFxe90RfuZjbbClFbm/tU7RmycHqciPXViI35tToF1CXMJsxd7q6M2iaXKc=</InverseQ><D>HVnfO/gBreRDJzOjDzFUDDOMK+F05qGJqMjj5sjUtUFOd9xYqLQ9Y3FoJuh3Ep4qKkEUSlTYAZdXbuYU+SJXBdw3KgAE+2YK6CUQ8XAy0ESaastm3U7wF/fxn8wjchmj07LS/4RwoycmQqD+7H3CZ1gZBwYILKGrzRBere4nCj/1i5LTbfweAMUo85KMfZDbGChlJUhd4vNiRPGmOeKCT1/xDAw/3ZKfUbhUjzBxg/1PThhLtv2wYEdkLpUq1RZmlJACtDD++fkt9x19UecfMpX7NmI43WLoc1x7ydtinrIO0b0NhFStXAPEQXlYyE4JvOSqIxJIbb/E7Vl5okVxOQ==</D></RSAKeyValue>";//my private key
  objRsaCrypto.FromXmlString(xmlString);
string cyphertextyear ="mell442PqhwZRDvAVawKhtspVWFsVG6x/6v7BzcaDvOFWImXOiq3hCZq6N0i7UpCkV8YVLLS/LTarWrSgrqskfQnIwA+inZIhfZLm3odUrYpBCMXJh9Y7s+6ugqiwpMu1xap9LBqhP7LdChwIV0c7GimgZKVVk7mZHBgmVOHRSx61RAx6HDkc0F7dfjBR+jUQR08knu4MUUNx7xQ6pSkg1MyTwrX4upMoodccBwni+cUFZWmIeEHazMMd2r6PkuwMvHkueFm0B4UsWnsqHtjgQuU5zmGx9rWpDIyDCKNTvWkTyB1lUrhpNk6qqeFZXVPPTsxfKcA0Pp2oz6ZF4ir";//my cypher text

 byte[] bytesCypherText = Convert.FromBase64String(cyphertextyear);
 byte[] bytesPlainTextData = objRsaCrypto.Decrypt(bytesCypherText, false);
  string strDecryptedVal = Encoding.ASCII.GetString(bytesPlainTextData);

I am using RSACryptoServiceProvider and decryption is working fine in windows 8 but failing in windows server 2012 r2 with below exception

System.Security.Cryptography.CryptographicException: Bad Data.

at System.Security.Cryptography.CryptographicException.ThrowCryptographicException(Int32 hr) at System.Security.Cryptography.RSACryptoServiceProvider.DecryptKey(SafeKeyHandle pKeyContext, Byte[] pbEncryptedKey, Int32 cbEncryptedKey, Boolean fOAEP, ObjectHandleOnStack ohRetDecryptedKey)
at System.Security.Cryptography.RSACryptoServiceProvider.Decrypt(Byte[] rgb, Boolean fOAEP)at

@ArtjomB thanks for responding. I have included the private key and cyphertext. — user3459002, Apr 04 '17 at 05:41
http://stackoverflow.com/questions/1496793/rsa-encryption-getting-bad-length — Waze Android, Apr 04 '17 at 06:31
Perhaps it is necessary to know which .Net version is installed. — Artjom B., Apr 04 '17 at 19:54
By the way, I found two online c# code execution sites where the [first decrypts correctly](http://ideone.com/y7c0bD) and the [second fails with bad data](http://csharppad.com/gist/fe84d5de8177e1884de0cbadb47b6dc7). — Artjom B., Apr 04 '17 at 20:01
@ArtjomB.Thanks for responding. application is using .Net 4.0. — user3459002, Apr 05 '17 at 07:07
@user3459002, were you able to resolve this by any chance? I am also facing similar issue, but with 1024 bit, the decryption works fine in Windows 7, but fails in Windows 10 & Windows Server 2012. Let me know. — Vasan, Jun 12 '17 at 13:03

score 1 · Answer 1 · answered Dec 23 '17 at 18:51

Your ciphertext is too short.

The length of bytesCypherText is 255, but your 2048-bit key produces a 256-byte response.

It seems that previous versions of Windows accepted too short and effectively prepended the value with extra zero bytes, and that they stopped doing that. (Most likely the original CAPI providers had the behavior of accepting "too short", but they have since been replaced with calls into the same backend that drives CNG; and it probably only accepts correctly sized data.)

If your ciphertext base64 were

AJnpZeONj6ocGUQ7wFWsCobbKVVhbFRusf+r+wc3Gg7zhViJlzoqt4QmaujdIu1KQpFfGFSy0vy02q1q
0oK6rJH0JyMAPop2SIX2S5t6HVK2KQQjFyYfWO7PuroKosKTLtcWqfSwaoT+y3QocCFdHOxopoGSlVZO
5mRwYJlTh0UsetUQMehw5HNBe3X4wUfo1EEdPJJ7uDFFDce8UOqUpINTMk8K1+LqTKKHXHAcJ4vnFBWV
piHhB2szDHdq+j5LsDLx5LnhZtAeFLFp7Kh7Y4ELlOc5hsfa1qQyMgwijU71pE8gdZVK4aTZOqqnhWV1
Tz07MXynAND6dqM+mReIqw==

You'll likely have better luck.

Alternatively:

if (bytesCypherText.Length * 8 < objRsaCrypto.KeySize)
{
    byte[] tmp = new byte[objRsaCrypto.KeySize / 8];
    Buffer.BlockCopy(
        bytesCypherText,
        0,
        tmp,
        tmp.Length - bytesCypherText.Length,
        bytesCypherText.Length);

    bytesCypherText = tmp;
}

byte[] bytesPlainTextData = objRsaCrypto.Decrypt(bytesCypherText, false);

RSA decryption with 2048 bit key is giving bad data for encrypted text of length 340 on windows server 2012 r2,while it is working fine on windows 8

1 Answers1