com.jcraft.jsch

Interface DH

public interface DH

Usually not to be used by applications. The implementation of the cryptographic algorithms in the Diffie-Hellman key exchange.

The group in question here is the multiplicative group of the finite field with p elements. It (or at least a quite large subgroup of it) should be generated by g.

Here is a short view of the algorithm (which would work in any group which we could somehow encode as numbers, by the way):

• We generate a random number x, calculate e = g^x and send e to the server.
• The server generates a random number y, calculates f = g^y and sends us f.
• We can know calculate {@code K = f^x}, while the server calculates K = e^y (and since multiplication of integers is commutative, e^y = (g^x)^y = g^(x*y) = g^(y*x) = (g^y)^x = f^x, both have the same number.)

The methods of this interface will generally be called in the order defined here, each once.

The implementing class has to do the random number generation of x and the modular arithmetic.

The implementing class will be chosen by the configuration option "dh", a default implementation is delivered with the library.

See Also:

RFC 4253, section 8. Diffie-Hellman Key Exchange, RFC 4419, Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol

Method Summary

Modifier and Type	Method and Description
void	checkRange()
byte[]	getE() Retrieves the value e, that is the result of g^x mod P.
byte[]	getK() Retrieves the secret number K which was created by the key exchange and will be used to create the key.
void	init() initializes the algorithm object for a new exchange.
void	setF(byte[] f) Sets the value of f, that is the result of g^y mod P
void	setG(byte[] g) Sets the generator of the group.
void	setP(byte[] p) Sets the prime number, modulo which the calculations should be done.

Method Detail

init

void init()
   throws Exception

initializes the algorithm object for a new exchange.

Throws:

Exception

setP

void setP(byte[] p)

Sets the prime number, modulo which the calculations should be done.

setG

void setG(byte[] g)

Sets the generator of the group. (This will be most often 2 or another small prime.)

getE

byte[] getE()
     throws Exception

Retrieves the value e, that is the result of g^x mod P.

Throws:

Exception

setF

void setF(byte[] f)

Sets the value of f, that is the result of g^y mod P

getK

byte[] getK()
     throws Exception

Retrieves the secret number K which was created by the key exchange and will be used to create the key.

Throws:

Exception

checkRange

void checkRange()
         throws Exception

Throws:

Exception