Add frontend, backend and CLI

cli/packages/srp/server.go

@@ -0,0 +1,104 @@
+package srp
+
+import (
+	"bytes"
+	"errors"
+	"math/big"
+)
+
+type SRPServer struct {
+	Params   *SRPParams
+	Verifier *big.Int
+	Secret2  *big.Int
+	B        *big.Int
+	M1       []byte
+	M2       []byte
+	K        []byte
+	u        *big.Int
+	s        *big.Int
+}
+
+func NewServer(params *SRPParams, Vb []byte, S2b []byte) *SRPServer {
+	multiplier := getMultiplier(params)
+	V := intFromBytes(Vb)
+	secret2 := intFromBytes(S2b)
+
+	Bb := getB(params, multiplier, V, secret2)
+	B := intFromBytes(Bb)
+
+	return &SRPServer{
+		Params:   params,
+		Secret2:  secret2,
+		Verifier: V,
+		B:        B,
+	}
+}
+
+func (s *SRPServer) ComputeB() []byte {
+	return intToBytes(s.B)
+}
+
+func (s *SRPServer) SetA(A []byte) {
+	AInt := intFromBytes(A)
+	U := getu(s.Params, AInt, s.B)
+	S := serverGetS(s.Params, s.Verifier, AInt, s.Secret2, U)
+
+	s.K = getK(s.Params, S)
+	s.M1 = getM1(s.Params, A, intToBytes(s.B), S)
+	s.M2 = getM2(s.Params, A, s.M1, s.K)
+
+	s.u = U               // only for tests
+	s.s = intFromBytes(S) // only for tests
+}
+
+func (s *SRPServer) CheckM1(M1 []byte) ([]byte, error) {
+	if !bytes.Equal(s.M1, M1) {
+		return nil, errors.New("Client did not use the same password")
+	} else {
+		return s.M2, nil
+	}
+}
+
+func (s *SRPServer) ComputeK() []byte {
+	return s.K
+}
+
+// Helpers
+
+func serverGetS(params *SRPParams, V, A, S2, U *big.Int) []byte {
+	ALessThan0 := A.Cmp(big.NewInt(0)) <= 0
+	NLessThanA := params.N.Cmp(A) <= 0
+	if ALessThan0 || NLessThanA {
+		panic("invalid client-supplied 'A', must be 1..N-1")
+	}
+
+	result1 := new(big.Int)
+	result1.Exp(V, U, params.N)
+
+	result2 := new(big.Int)
+	result2.Mul(A, result1)
+
+	result3 := new(big.Int)
+	result3.Exp(result2, S2, params.N)
+
+	result4 := new(big.Int)
+	result4.Mod(result3, params.N)
+
+	return padToN(result4, params)
+}
+
+func getB(params *SRPParams, multiplier, V, b *big.Int) []byte {
+	gModPowB := new(big.Int)
+	gModPowB.Exp(params.G, b, params.N)
+
+	kMulV := new(big.Int)
+	kMulV.Mul(multiplier, V)
+
+	leftSide := new(big.Int)
+	leftSide.Add(kMulV, gModPowB)
+
+	final := new(big.Int)
+	final.Mod(leftSide, params.N)
+
+	return padToN(final, params)
+}