CODEWITHSUNDEEP
c#.netcryptographyrsablackberry-jde
jim
jim

Reputation: 9138

Decrypt PKCS #1 v2.1 cipher from BlackBerry in C#.NET

I have written a BlackBerry app that RSA encrypts a message using PKCS1FormatterEngine. This outputs a ciphered message formatted in PKCS #1 v2.1

Here is a snippet of the message:

ç½.¦B¯€ü6Áùε"aYÅÂ7;«&â/Ѥ²•¨S.°.b7<iÔ½Œ.:.Ý&D‹±ì‰8.V•.Ä$‡ZAÜ.p.Ø}åÜ.uK.Æøæ

I already have the RSA private key in .NET but I can't seem to find a way to decrypt this.

Any ideas on classes I should use etc would be greatly appreciated.

Upvotes: 2

Views: 1764

Answers (5)

Narut Udomchoke
Narut Udomchoke

Reputation: 1

var encryptedtext = csp.Encrypt(plaintext, true);  //Set OAEP=True
var decryptedtext = csp.Decrypt(plaintext, true);  //Set OAEP=True

Upvotes: 0

jim
jim

Reputation: 9138

I'm using the RSACryptoServiceProvider .NET class with the function Decrypt.

The first paramater is the encrypted data and the second, a boolean specifies which padding type to use.

True = OAEP padding (PKCS#1 v2.1) False = PKCS#1 v1.5

It is strange because my code worked when it set it the parameter to false. I'm pretty sure the cipher is in PKCS#1 v2.1 because i'm using this class from the BlackBerry SDK.

Quote from the API document:

We implemented the PKCS1 formatter engine as per the PKCS #1 version 2.1 document.

In any case, it works for me now. Hope this helps somebody else. :)

Upvotes: 0

Rasmus Faber
Rasmus Faber

Reputation: 49677

PKCS#1 v2.1 has two encryption modes: RSAES-OAEP and RSAES-PKCS1-V1_5.

RSAES-PKCS1-V1_5 was also included in earlier versions of the standard, so it is often also called PKCS#1 v.1.5. It is therefore not uncommon to refer to RSAES-OAEP as PKCS#1 v.2.1 - but it is incorrect and errorprone.

In the documentation for PKCS1FormatterEngine, RIM documents that it has implemented PKCS#1 according to PKCS#1 v.2.1, but do not explain whether they mean RSAES-OAEP or RSAES-PKCS1-V1_5.

But since you report that RSACryptoServiceProvider.Decrypt(array, false); works, I would conclude that they have implemented RSAES-PKCS1-V1_5. Just use that: it is the easiest way to decrypt RSAES-PKCS1-V1_5. Alternatively, you can use RSAPKCS1KeyExchangeDeformatter.

Upvotes: 1

poupou
poupou

Reputation: 43553

Is there anything wrong with the standard RSAOAEPKeyExchangeDeformatter class ? if so then you should show us your code.

It's been in the .NET framework forever but was not available before Windows XP (e.g. Windows 2000) IIRC - but that should not be a huge problem today.

Upvotes: 1

Maarten Bodewes
Maarten Bodewes

Reputation: 94038

Bouncy Castle seems to be able to use OAEP mode of RSA encryption/decryption. Never tried it though, I'm only using the Java libs of Bouncy.

Ah, found an example, see the sample code on the bottom of the page:

http://www.go4expert.com/forums/showthread.php?t=24827

Upvotes: 0

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