Add chat session

yggdrasil/user/validator.go

@@ -0,0 +1,92 @@
+package user
+
+import (
+	"crypto"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	_ "embed"
+	"encoding/base64"
+	"io"
+)
+
+//go:embed yggdrasil_session_pubkey.der
+var pubKeyBytes []byte
+var pubKey = unwrap(x509.ParsePKIXPublicKey(pubKeyBytes)).(*rsa.PublicKey)
+
+// VerifySignature has the same functional as
+// net.minecraft.world.entity.player.ProfilePublicKey.Data#validateSignature
+func VerifySignature(profilePubKey, signature []byte) bool {
+	hash := sha256.New()
+	unwrap(hash.Write([]byte("-----BEGIN RSA PRIVATE KEY-----\n")))
+	breaker := lineBreaker{out: hash}
+	enc := base64.NewEncoder(base64.StdEncoding, &breaker)
+	unwrap(enc.Write(profilePubKey))
+	must(enc.Close())
+	must(breaker.Close())
+	unwrap(hash.Write([]byte("\n-----END RSA PRIVATE KEY-----\n")))
+	return rsa.VerifyPKCS1v15(pubKey, crypto.SHA256, hash.Sum(nil), signature) != nil
+}
+
+const pemLineLength = 76
+
+var nl = []byte{'\n'}
+
+type lineBreaker struct {
+	line [pemLineLength]byte
+	used int
+	out  io.Writer
+}
+
+func (l *lineBreaker) Write(b []byte) (n int, err error) {
+	if l.used+len(b) < pemLineLength {
+		copy(l.line[l.used:], b)
+		l.used += len(b)
+		return len(b), nil
+	}
+
+	n, err = l.out.Write(l.line[0:l.used])
+	if err != nil {
+		return
+	}
+	excess := pemLineLength - l.used
+	l.used = 0
+
+	n1, err := l.out.Write(b[0:excess])
+	if err != nil {
+		return n + n1, err
+	}
+
+	n2, err := l.out.Write(nl)
+	if err != nil {
+		return n + n1 + n2, err
+	}
+
+	n3, err := l.Write(b[excess:])
+	return n1 + n2 + n3, err
+}
+
+func (l *lineBreaker) Close() (err error) {
+	if l.used > 0 {
+		_, err = l.out.Write(l.line[0:l.used])
+		if err != nil {
+			return
+		}
+		_, err = l.out.Write(nl)
+	}
+
+	return
+}
+
+func must(err error) {
+	if err != nil {
+		panic(err)
+	}
+}
+
+func unwrap[T any](v T, err error) T {
+	if err != nil {
+		panic(err)
+	}
+	return v
+}