Re: Encrypting using RSA private Key

Hi Jeronimo Bertran,

not with .NET! the answer is YES but only if you rewrite the rsa algo :-D
....you need a BigInteger library ;-)

P = 1st large prime number
Q = 2nd large prime number
E = Public Exponent: 3 (fast operation), 65537 (secure) (or random number
which must: GCD(E, (P-1)*(Q-1))==1)
N = Public Modulus, N=P*Q
D = Private Exponent: D=E^(-1) mod ((P-1)*(Q-1))

{N,E}=publickey
{D}=privatekey

standard use:
-------------
encryption: C=M^E mod N with M<N
decryption: M=C^D mod N

the inverse use of rsa :-o is:

encryption: C=M^D mod N with M<N
decryption: M=C^E mod N

^ = PowerOf

HTH
--
Marcello Cantelmo
www.cantelmosoftware.com

Hi,

Is it possible to encrypt using the RSA private key and decrypt using the
public key? I am able to do the opposite but when I try to decrypt using
the private key I get a "Bad Key" Exception. Here is an example:

rsa = new RSACryptoServiceProvider();
RSAParameters publicKey = rsa.ExportParameters(false);
RSAParameters privateKey = rsa.ExportParameters(true);
byte[] testPlainData = new byte[] { 0x01, 0x02, 0x03 };
rsa.ImportParameters(publicKey);
byte[] enc = rsa.Encrypt(testPlainData, false);
rsa.ImportParameters(privateKey);
byte[] plain = rsa.Decrypt(enc, false);

enc = rsa.Encrypt(testPlainData, false);
rsa.ImportParameters(publicKey);
rsa.Decrypt(enc, false);

The first encryption and decryption work fine. The second encryption
(using the private key) seems to work but the decryption using the public
key throws the exception.

Thanks,

Jeronimo


.

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