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// Copyright © 2022 siddharth <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
package lib
import "math/big"
// SRP - implementation.
// Reference http://srp.stanford.edu/design.html
// SRP Client UI - Spec
//
// > register s@ricketyspace.net
// Enter password
// > ******
// Registering with server...registered!
// > login s@ricketyspace.net
// Enter password
// > ******
// Logging in...in!
// s@ricketyspace.net>
// s@ricketyspace.net> login s@ricketyspace.net
// login command not allowed when logged in
// s@ricketyspace.net> register rsd@gnu.org
// register command not allowed when logged in
// s@ricketyspace.net> logout
// Logging out..out!
// > register s@ricketyspace.net
// Already registered!
// SRP Server.
type SRPServer struct {
users []SRPUser
}
// Registered user on the SRP server.
type SRPUser struct {
// Large safe prime. Server and client agree upon the value of
// N.
n *big.Int
// Generator modulo N. Server and client agree upon the value
// of N.
g *big.Int
// Multipier parameter. Server and client agree upon the value
// of N.
k *big.Int
// Hashing object for H() function.
h Sha256
// User's email address
ident string
// Salt. Randomly generator by the server.
salt []byte
// Private key derived from salt and user's pass.
x *big.Int
// Scrambling parameter.
u *big.Int
// Secret ephemeral value.
b *big.Int
// Password verifier.
v *big.Int
// Session key.
sk []byte
}
// SRP client.
type SRPClient struct {
session SRPClientSession
}
// User session on the SRP client.
type SRPClientSession struct {
// Large safe prime. Client and server agree upon the value of
// N.
n *big.Int
// Generator modulo N. Client and server agree upon the value
// of N.
g *big.Int
// Multipier parameter. Client and server agree upon the value
// of N.
k *big.Int
// User's email address
ident string
// Scrambling parameter.
u *big.Int
// Secret ephemeral value.
a *big.Int
// Session key.
sk []byte
}
func NewSRPUser(n, g, k, ident, pass string) (*SRPUser, error) {
var err error
var ok bool
user := new(SRPUser)
user.n, ok = new(big.Int).SetString(StripSpaceChars(n), 16)
if !ok {
return nil, CPError{"n is invalid"}
}
user.g, ok = new(big.Int).SetString(StripSpaceChars(g), 16)
if !ok {
return nil, CPError{"g is invalid"}
}
user.k, ok = new(big.Int).SetString(StripSpaceChars(k), 16)
if !ok {
return nil, CPError{"k is invalid"}
}
user.ident = ident
user.x = big.NewInt(0)
user.v = big.NewInt(0)
// Initialize hashing object.
user.h = Sha256{}
user.h.Init([]uint32{})
// Generate salt.
user.salt, err = RandomBytes(8)
if err != nil {
return nil, err
}
// Generate private key `x` from salt+pass
m := make([]byte, 0)
copy(m, user.salt)
m = append(m, StrToBytes(pass)...)
user.h.Message(m)
user.x.SetBytes(user.h.Hash())
// Generate password verifier `v`
user.v.Exp(user.g, user.x, user.n)
return user, nil
}
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