refactor: Split keys and keyext packages, make compression, signature and encryption packages public

pkg/encryption/decrypt.go

@@ -0,0 +1,141 @@
+package encryption
+
+import (
+	"archive/tar"
+	"bytes"
+	"encoding/base64"
+	"encoding/json"
+	"io"
+
+	"filippo.io/age"
+	"github.com/ProtonMail/go-crypto/openpgp"
+	"github.com/pojntfx/stfs/internal/records"
+	"github.com/pojntfx/stfs/pkg/config"
+)
+
+func Decrypt(
+	src io.Reader,
+	encryptionFormat string,
+	identity interface{},
+) (io.ReadCloser, error) {
+	switch encryptionFormat {
+	case config.EncryptionFormatAgeKey:
+		identity, ok := identity.(*age.X25519Identity)
+		if !ok {
+			return nil, config.ErrIdentityUnparsable
+		}
+
+		r, err := age.Decrypt(src, identity)
+		if err != nil {
+			return nil, err
+		}
+
+		return io.NopCloser(r), nil
+	case config.EncryptionFormatPGPKey:
+		identity, ok := identity.(openpgp.EntityList)
+		if !ok {
+			return nil, config.ErrIdentityUnparsable
+		}
+
+		r, err := openpgp.ReadMessage(src, identity, nil, nil)
+		if err != nil {
+			return nil, err
+		}
+
+		return io.NopCloser(r.UnverifiedBody), nil
+	case config.NoneKey:
+		return io.NopCloser(src), nil
+	default:
+		return nil, config.ErrEncryptionFormatUnsupported
+	}
+}
+
+func DecryptHeader(
+	hdr *tar.Header,
+	encryptionFormat string,
+	identity interface{},
+) error {
+	if encryptionFormat == config.NoneKey {
+		return nil
+	}
+
+	if hdr.PAXRecords == nil {
+		return config.ErrTarHeaderEmbeddedMissing
+	}
+
+	encryptedEmbeddedHeader, ok := hdr.PAXRecords[records.STFSRecordEmbeddedHeader]
+	if !ok {
+		return config.ErrTarHeaderEmbeddedMissing
+	}
+
+	embeddedHeader, err := DecryptString(encryptedEmbeddedHeader, encryptionFormat, identity)
+	if err != nil {
+		return err
+	}
+
+	var newHdr tar.Header
+	if err := json.Unmarshal([]byte(embeddedHeader), &newHdr); err != nil {
+		return err
+	}
+
+	*hdr = newHdr
+
+	return nil
+}
+
+func DecryptString(
+	src string,
+	encryptionFormat string,
+	identity interface{},
+) (string, error) {
+	switch encryptionFormat {
+	case config.EncryptionFormatAgeKey:
+		identity, ok := identity.(*age.X25519Identity)
+		if !ok {
+			return "", config.ErrIdentityUnparsable
+		}
+
+		decoded, err := base64.StdEncoding.DecodeString(src)
+		if err != nil {
+			return "", err
+		}
+
+		r, err := age.Decrypt(bytes.NewBufferString(string(decoded)), identity)
+		if err != nil {
+			return "", err
+		}
+
+		out := &bytes.Buffer{}
+		if _, err := io.Copy(out, r); err != nil {
+			return "", err
+		}
+
+		return out.String(), nil
+	case config.EncryptionFormatPGPKey:
+		identity, ok := identity.(openpgp.EntityList)
+		if !ok {
+			return "", config.ErrIdentityUnparsable
+		}
+
+		decoded, err := base64.StdEncoding.DecodeString(src)
+		if err != nil {
+			return "", err
+		}
+
+		r, err := openpgp.ReadMessage(bytes.NewBufferString(string(decoded)), identity, nil, nil)
+		if err != nil {
+			return "", err
+		}
+
+		out := &bytes.Buffer{}
+		if _, err := io.Copy(out, r.UnverifiedBody); err != nil {
+			return "", err
+		}
+
+		return out.String(), nil
+	case config.NoneKey:
+		return src, nil
+	default:
+		return "", config.ErrEncryptionFormatUnsupported
+	}
+}