[IMPLEMENTATION] DSA algorithm implementation (#737)

Co-authored-by: Rak Laptudirm <[email protected]>

Author: ddaniel27

cipher/dsa/dsa.go

@@ -0,0 +1,196 @@
+/*
+dsa.go
+description: DSA encryption and decryption including key generation
+details: [DSA wiki](https://en.wikipedia.org/wiki/Digital_Signature_Algorithm)
+author(s): [ddaniel27](https://github.com/ddaniel27)
+*/
+package dsa
+
+import (
+	"crypto/rand"
+	"io"
+	"math/big"
+)
+
+const (
+	numMRTests = 64   // Number of Miller-Rabin tests
+	L          = 1024 // Number of bits in p
+	N          = 160  // Number of bits in q
+)
+
+type (
+	// parameters represents the DSA parameters
+	parameters struct {
+		P, Q, G *big.Int
+	}
+
+	// dsa represents the DSA
+	dsa struct {
+		parameters
+		pubKey  *big.Int // public key (y)
+		privKey *big.Int // private key (x)
+	}
+)
+
+// New creates a new DSA instance
+func New() *dsa {
+	d := new(dsa)
+	d.dsaParameterGeneration()
+	d.keyGen()
+	return d
+}
+
+// Parameter generation for DSA
+// 1. FIPS 186-4 specifies that the L and N values must be (1024, 160), (2048, 224), or (3072, 256)
+// 2. Choose a N-bit prime q
+// 3. Choose a L-bit prime p such that p-1 is a multiple of q
+// 4. Choose an integer h randomly from the range [2, p-2]
+// 5. Compute g = h^((p-1)/q) mod p
+// 6. Return (p, q, g)
+func (dsa *dsa) dsaParameterGeneration() {
+	var err error
+	p, q, bigInt := new(big.Int), new(big.Int), new(big.Int)
+	one, g, h := big.NewInt(1), big.NewInt(1), big.NewInt(2)
+	pBytes := make([]byte, L/8)
+
+	// GPLoop is a label for the loop
+	// We use this loop to change the prime q if we don't find a prime p
+GPLoop:
+	for {
+		// 2. Choose a N-bit prime q
+		q, err = rand.Prime(rand.Reader, N)
+		if err != nil {
+			panic(err)
+		}
+
+		for i := 0; i < 4*L; i++ {
+			// 3. Choose a L-bit prime p such that p-1 is a multiple of q
+			// In this case we generate a random number of L bits
+			if _, err := io.ReadFull(rand.Reader, pBytes); err != nil {
+				panic(err)
+			}
+
+			// This are the minimum conditions for p being a possible prime
+			pBytes[len(pBytes)-1] |= 1 // p is odd
+			pBytes[0] |= 0x80          // p has the highest bit set
+			p.SetBytes(pBytes)
+
+			// Instead of using (p-1)%q == 0
+			// We ensure that p-1 is a multiple of q and validates if p is prime
+			bigInt.Mod(p, q)
+			bigInt.Sub(bigInt, one)
+			p.Sub(p, bigInt)
+			if p.BitLen() < L || !p.ProbablyPrime(numMRTests) { // Check if p is prime and has L bits
+				continue
+			}
+
+			dsa.P = p
+			dsa.Q = q
+			break GPLoop
+		}
+	}
+
+	// 4. Choose an integer h randomly from the range [2, p-2]. Commonly, h = 2
+	// 5. Compute g = h^((p-1)/q) mod p. In case g == 1, increment h until g != 1
+	pm1 := new(big.Int).Sub(p, one)
+
+	for g.Cmp(one) == 0 {
+		g.Exp(h, new(big.Int).Div(pm1, q), p)
+		h.Add(h, one)
+	}
+
+	dsa.G = g
+}
+
+// keyGen is key generation for DSA
+// 1. Choose a random integer x from the range [1, q-1]
+// 2. Compute y = g^x mod p
+func (dsa *dsa) keyGen() {
+	// 1. Choose a random integer x from the range [1, q-1]
+	x, err := rand.Int(rand.Reader, new(big.Int).Sub(dsa.Q, big.NewInt(1)))
+	if err != nil {
+		panic(err)
+	}
+
+	dsa.privKey = x
+
+	// 2. Compute y = g^x mod p
+	dsa.pubKey = new(big.Int).Exp(dsa.G, x, dsa.P)
+}
+
+// Sign is signature generation for DSA
+// 1. Choose a random integer k from the range [1, q-1]
+// 2. Compute r = (g^k mod p) mod q
+// 3. Compute s = (k^-1 * (H(m) + x*r)) mod q
+func Sign(m []byte, p, q, g, x *big.Int) (r, s *big.Int) {
+	// 1. Choose a random integer k from the range [1, q-1]
+	k, err := rand.Int(rand.Reader, new(big.Int).Sub(q, big.NewInt(1)))
+	if err != nil {
+		panic(err)
+	}
+
+	// 2. Compute r = (g^k mod p) mod q
+	r = new(big.Int).Exp(g, k, p)
+	r.Mod(r, q)
+
+	// 3. Compute s = (k^-1 * (H(m) + x*r)) mod q
+	h := new(big.Int).SetBytes(m)     // This should be the hash of the message
+	s = new(big.Int).ModInverse(k, q) // k^-1 mod q
+	s.Mul(
+		s,
+		new(big.Int).Add( // (H(m) + x*r)
+			h,
+			new(big.Int).Mul(x, r),
+		),
+	)
+	s.Mod(s, q) // mod q
+
+	return r, s
+}
+
+// Verify is signature verification for DSA
+// 1. Compute w = s^-1 mod q
+// 2. Compute u1 = (H(m) * w) mod q
+// 3. Compute u2 = (r * w) mod q
+// 4. Compute v = ((g^u1 * y^u2) mod p) mod q
+// 5. If v == r, the signature is valid
+func Verify(m []byte, r, s, p, q, g, y *big.Int) bool {
+	// 1. Compute w = s^-1 mod q
+	w := new(big.Int).ModInverse(s, q)
+
+	// 2. Compute u1 = (H(m) * w) mod q
+	h := new(big.Int).SetBytes(m) // This should be the hash of the message
+	u1 := new(big.Int).Mul(h, w)
+	u1.Mod(u1, q)
+
+	// 3. Compute u2 = (r * w) mod q
+	u2 := new(big.Int).Mul(r, w)
+	u2.Mod(u2, q)
+
+	// 4. Compute v = ((g^u1 * y^u2) mod p) mod q
+	v := new(big.Int).Exp(g, u1, p)
+	v.Mul(
+		v,
+		new(big.Int).Exp(y, u2, p),
+	)
+	v.Mod(v, p)
+	v.Mod(v, q)
+
+	// 5. If v == r, the signature is valid
+	return v.Cmp(r) == 0
+}
+
+// GetPublicKey returns the public key (y)
+func (dsa *dsa) GetPublicKey() *big.Int {
+	return dsa.pubKey
+}
+
+// GetParameters returns the DSA parameters (p, q, g)
+func (dsa *dsa) GetParameters() parameters {
+	return dsa.parameters
+}
+
+// GetPrivateKey returns the private Key (x)
+func (dsa *dsa) GetPrivateKey() *big.Int {
+	return dsa.privKey
+}

cipher/dsa/dsa_test.go

@@ -0,0 +1,114 @@
+package dsa_test
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/TheAlgorithms/Go/cipher/dsa"
+)
+
+func TestDSA(t *testing.T) {
+	tests := []struct {
+		name    string
+		message string
+		alter   bool
+		want    bool
+	}{
+		{
+			name:    "valid signature",
+			message: "Hello, world!",
+			alter:   false,
+			want:    true,
+		},
+		{
+			name:    "invalid signature",
+			message: "Hello, world!",
+			alter:   true,
+			want:    false,
+		},
+	}
+	// Generate a DSA key pair
+	dsaInstance := dsa.New()
+	pubKey := dsaInstance.GetPublicKey()
+	params := dsaInstance.GetParameters()
+	privKey := dsaInstance.GetPrivateKey()
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+
+			// Sign the message
+			r, s := dsa.Sign(
+				[]byte(tt.message),
+				params.P,
+				params.Q,
+				params.G,
+				privKey,
+			)
+
+			if tt.alter {
+				// Alter the signature
+				r.Add(r, big.NewInt(1))
+			}
+
+			// Verify the signature
+			if got := dsa.Verify(
+				[]byte(tt.message),
+				r,
+				s,
+				params.P,
+				params.Q,
+				params.G,
+				pubKey,
+			); got != tt.want {
+				t.Errorf("got %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+/* ------------------- BENCHMARKS ------------------- */
+func BenchmarkDSANew(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		dsa.New()
+	}
+}
+
+func BenchmarkDSASign(b *testing.B) {
+	dsaInstance := dsa.New()
+	params := dsaInstance.GetParameters()
+	privKey := dsaInstance.GetPrivateKey()
+	for i := 0; i < b.N; i++ {
+		dsa.Sign(
+			[]byte("Hello, World!"),
+			params.P,
+			params.Q,
+			params.G,
+			privKey,
+		)
+	}
+}
+
+func BenchmarkDSAVerify(b *testing.B) {
+	dsaInstance := dsa.New()
+	pubKey := dsaInstance.GetPublicKey()
+	params := dsaInstance.GetParameters()
+	privKey := dsaInstance.GetPrivateKey()
+	r, s := dsa.Sign(
+		[]byte("Hello, World!"),
+		params.P,
+		params.Q,
+		params.G,
+		privKey,
+	)
+	for i := 0; i < b.N; i++ {
+		dsa.Verify(
+			[]byte("Hello, World!"),
+			r,
+			s,
+			params.P,
+			params.Q,
+			params.G,
+			pubKey,
+		)
+	}
+}