Add client_ed25519 authentication

- Implements the necessary client code for [ed25519 authentication](https://mariadb.com/kb/en/authentication-plugin-ed25519/).
- Add a test directly from the reference implementation to verify it
works.
- A continuation of #1220,
but doesn't use CGO.
- This patch uses filippo.io/edwards25519 to implement the crypto bits.
The standard library `crypto/ed25519` cannot be used as MariaDB chose
a scheme that is simply not compatible with what the standard library
provides.

Author: Gusted

Diff for: AUTHORS

@@ -39,6 +39,7 @@ Evan Elias <evan at skeema.net>
 Evan Shaw <evan at vendhq.com>
 Frederick Mayle <frederickmayle at gmail.com>
 Gustavo Kristic <gkristic at gmail.com>
+Gusted <postmaster at gusted.xyz>
 Hajime Nakagami <nakagami at gmail.com>
 Hanno Braun <mail at hannobraun.com>
 Henri Yandell <flamefew at gmail.com>

Diff for: auth.go

@@ -13,10 +13,13 @@ import (
 	"crypto/rsa"
 	"crypto/sha1"
 	"crypto/sha256"
+	"crypto/sha512"
 	"crypto/x509"
 	"encoding/pem"
 	"fmt"
 	"sync"
+
+	"filippo.io/edwards25519"
 )
 
 // server pub keys registry
@@ -225,6 +228,44 @@ func encryptPassword(password string, seed []byte, pub *rsa.PublicKey) ([]byte,
 	return rsa.EncryptOAEP(sha1, rand.Reader, pub, plain, nil)
 }
 
+// Derived from https://github.com/MariaDB/server/blob/d8e6bb00888b1f82c031938f4c8ac5d97f6874c3/plugin/auth_ed25519/ref10/sign.c
+func doEd25519Auth(scramble []byte, password string) ([]byte, error) {
+	h := sha512.Sum512([]byte(password))
+
+	s, err := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
+	if err != nil {
+		return nil, err
+	}
+
+	nonceHash := sha512.New()
+	nonceHash.Write(h[32:])
+	nonceHash.Write(scramble)
+	nonce := nonceHash.Sum(nil)
+
+	r, err := edwards25519.NewScalar().SetUniformBytes(nonce)
+	if err != nil {
+		return nil, err
+	}
+	R := (&edwards25519.Point{}).ScalarBaseMult(r)
+
+	A := (&edwards25519.Point{}).ScalarBaseMult(s)
+
+	kHash := sha512.New()
+	kHash.Write(R.Bytes())
+	kHash.Write(A.Bytes())
+	kHash.Write(scramble)
+	k := kHash.Sum(nil)
+
+	K, err := edwards25519.NewScalar().SetUniformBytes(k)
+	if err != nil {
+		return nil, err
+	}
+
+	S := K.MultiplyAdd(K, s, r)
+
+	return append(R.Bytes(), S.Bytes()...), nil
+}
+
 func (mc *mysqlConn) sendEncryptedPassword(seed []byte, pub *rsa.PublicKey) error {
 	enc, err := encryptPassword(mc.cfg.Passwd, seed, pub)
 	if err != nil {
@@ -290,6 +331,13 @@ func (mc *mysqlConn) auth(authData []byte, plugin string) ([]byte, error) {
 		enc, err := encryptPassword(mc.cfg.Passwd, authData, pubKey)
 		return enc, err
 
+	case "client_ed25519":
+		if len(authData) != 32 {
+			return nil, ErrMalformPkt
+		}
+
+		return doEd25519Auth(authData, mc.cfg.Passwd)
+
 	default:
 		mc.cfg.Logger.Print("unknown auth plugin:", plugin)
 		return nil, ErrUnknownPlugin

Diff for: auth_test.go

@@ -1328,3 +1328,54 @@ func TestAuthSwitchSHA256PasswordSecure(t *testing.T) {
 		t.Errorf("got unexpected data: %v", conn.written)
 	}
 }
+
+// Derived from https://github.com/MariaDB/server/blob/6b2287fff23fbdc362499501c562f01d0d2db52e/plugin/auth_ed25519/ed25519-t.c
+func TestEd25519Auth(t *testing.T) {
+	conn, mc := newRWMockConn(1)
+	mc.cfg.User = "root"
+	mc.cfg.Passwd = "foobar"
+
+	authData := []byte("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA")
+	plugin := "client_ed25519"
+
+	// Send Client Authentication Packet
+	authResp, err := mc.auth(authData, plugin)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = mc.writeHandshakeResponsePacket(authResp, plugin)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// check written auth response
+	authRespStart := 4 + 4 + 4 + 1 + 23 + len(mc.cfg.User) + 1
+	authRespEnd := authRespStart + 1 + len(authResp)
+	writtenAuthRespLen := conn.written[authRespStart]
+	writtenAuthResp := conn.written[authRespStart+1 : authRespEnd]
+	expectedAuthResp := []byte{
+		232, 61, 201, 63, 67, 63, 51, 53, 86, 73, 238, 35, 170, 117, 146,
+		214, 26, 17, 35, 9, 8, 132, 245, 141, 48, 99, 66, 58, 36, 228, 48,
+		84, 115, 254, 187, 168, 88, 162, 249, 57, 35, 85, 79, 238, 167, 106,
+		68, 117, 56, 135, 171, 47, 20, 14, 133, 79, 15, 229, 124, 160, 176,
+		100, 138, 14,
+	}
+	if writtenAuthRespLen != 64 {
+		t.Fatalf("expected 64 bytes from client, got %d", writtenAuthRespLen)
+	}
+	if !bytes.Equal(writtenAuthResp, expectedAuthResp) {
+		t.Fatalf("auth response did not match expected value:\n%v\n%v", writtenAuthResp, expectedAuthResp)
+	}
+	conn.written = nil
+
+	// auth response
+	conn.data = []byte{
+		7, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, // OK
+	}
+	conn.maxReads = 1
+
+	// Handle response to auth packet
+	if err := mc.handleAuthResult(authData, plugin); err != nil {
+		t.Errorf("got error: %v", err)
+	}
+}

Diff for: go.mod

@@ -1,3 +1,5 @@
 module github.com/go-sql-driver/mysql
 
 go 1.18
+
+require filippo.io/edwards25519 v1.1.0

Diff for: go.sum

@@ -0,0 +1,2 @@
+filippo.io/edwards25519 v1.1.0 h1:FNf4tywRC1HmFuKW5xopWpigGjJKiJSV0Cqo0cJWDaA=
+filippo.io/edwards25519 v1.1.0/go.mod h1:BxyFTGdWcka3PhytdK4V28tE5sGfRvvvRV7EaN4VDT4=