Initial structure

internal/crypto/keys.go

@@ -0,0 +1,100 @@
+// Package crypto handles the RSA key material every node uses for
+// mutual TLS authentication and for the trust-store fingerprint pinning.
+//
+// Keys are RSA-3072 (NIST 112-bit security, well within the safe band
+// through ~2030). They live PEM-encoded under <data_dir>/keys/.
+package crypto
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/jasper/quptime/internal/config"
+)
+
+// KeySize is the RSA modulus size used by qu.
+const KeySize = 3072
+
+// GenerateKeyPair creates a fresh RSA keypair and writes the private,
+// public, and self-signed certificate to the standard paths.
+// It refuses to overwrite existing keys.
+func GenerateKeyPair(commonName string) (*rsa.PrivateKey, error) {
+	if _, err := os.Stat(config.PrivateKeyPath()); err == nil {
+		return nil, errors.New("key material already exists; refusing to overwrite")
+	}
+	if err := config.EnsureDataDir(); err != nil {
+		return nil, err
+	}
+	priv, err := rsa.GenerateKey(rand.Reader, KeySize)
+	if err != nil {
+		return nil, fmt.Errorf("generate rsa key: %w", err)
+	}
+	if err := writePEM(config.PrivateKeyPath(), "RSA PRIVATE KEY",
+		x509.MarshalPKCS1PrivateKey(priv), 0o600); err != nil {
+		return nil, err
+	}
+	pubDER, err := x509.MarshalPKIXPublicKey(&priv.PublicKey)
+	if err != nil {
+		return nil, err
+	}
+	if err := writePEM(config.PublicKeyPath(), "PUBLIC KEY", pubDER, 0o644); err != nil {
+		return nil, err
+	}
+	certDER, err := buildSelfSignedCert(priv, commonName)
+	if err != nil {
+		return nil, err
+	}
+	if err := writePEM(config.CertFilePath(), "CERTIFICATE", certDER, 0o644); err != nil {
+		return nil, err
+	}
+	return priv, nil
+}
+
+// LoadPrivateKey reads the on-disk RSA private key.
+func LoadPrivateKey() (*rsa.PrivateKey, error) {
+	raw, err := os.ReadFile(config.PrivateKeyPath())
+	if err != nil {
+		return nil, err
+	}
+	block, _ := pem.Decode(raw)
+	if block == nil {
+		return nil, errors.New("private key: no PEM block")
+	}
+	switch block.Type {
+	case "RSA PRIVATE KEY":
+		return x509.ParsePKCS1PrivateKey(block.Bytes)
+	case "PRIVATE KEY":
+		k, err := x509.ParsePKCS8PrivateKey(block.Bytes)
+		if err != nil {
+			return nil, err
+		}
+		rk, ok := k.(*rsa.PrivateKey)
+		if !ok {
+			return nil, errors.New("private key: not RSA")
+		}
+		return rk, nil
+	default:
+		return nil, fmt.Errorf("private key: unexpected PEM type %q", block.Type)
+	}
+}
+
+// LoadCertPEM reads the self-signed cert file (used as the TLS leaf).
+func LoadCertPEM() ([]byte, error) {
+	return os.ReadFile(config.CertFilePath())
+}
+
+// LoadPublicKeyPEM reads the public-key PEM (exchanged out of band
+// during invite / join).
+func LoadPublicKeyPEM() ([]byte, error) {
+	return os.ReadFile(config.PublicKeyPath())
+}
+
+func writePEM(path, blockType string, der []byte, perm os.FileMode) error {
+	encoded := pem.EncodeToMemory(&pem.Block{Type: blockType, Bytes: der})
+	return config.AtomicWrite(path, encoded, perm)
+}