From cac97aae6184f2f2af5ceeabeae7e2ced3481064 Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rosehogenson@posteo.net>
Date: Fri, 10 Oct 2025 22:37:41 -0700
Subject: Initial commit

---
 internal/sym/dec.go      | 106 +++++++++++++++++++++++++
 internal/sym/enc.go      | 102 ++++++++++++++++++++++++
 internal/sym/oae.go      | 203 +++++++++++++++++++++++++++++++++++++++++++++++
 internal/sym/pwhash.go   |  12 +++
 internal/sym/sym_test.go |  69 ++++++++++++++++
 5 files changed, 492 insertions(+)
 create mode 100644 internal/sym/dec.go
 create mode 100644 internal/sym/enc.go
 create mode 100644 internal/sym/oae.go
 create mode 100644 internal/sym/pwhash.go
 create mode 100644 internal/sym/sym_test.go

(limited to 'internal')

diff --git a/internal/sym/dec.go b/internal/sym/dec.go
new file mode 100644
index 0000000..7cbf5d4
--- /dev/null
+++ b/internal/sym/dec.go
@@ -0,0 +1,106 @@
+package sym
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+type lineReader struct {
+	r    bufio.Scanner
+	line []byte
+}
+
+func (r *lineReader) Read(buf []byte) (int, error) {
+	for len(r.line) == 0 {
+		if !r.r.Scan() {
+			if err := r.r.Err(); err != nil {
+				return 0, err
+			}
+			return 0, io.EOF
+		}
+		line := r.r.Bytes()
+		if bytes.HasPrefix(line, []byte("-")) {
+			continue
+		}
+		r.line = line
+	}
+	n := copy(buf, r.line)
+	r.line = r.line[n:]
+	return n, nil
+}
+
+type PasswordCache map[[SaltSize]byte][]byte
+
+func decryptBinary(w io.Writer, r io.Reader, password string, pwCache PasswordCache) error {
+	header := make([]byte, 1+SaltSize)
+	if _, err := io.ReadFull(r, header); err != nil {
+		return err
+	}
+	salt := header[1:]
+	key, ok := pwCache[[SaltSize]byte(salt)]
+	if !ok {
+		var err error
+		key, err = HashPassword(password, salt)
+		if err != nil {
+			return err
+		}
+		pwCache[[SaltSize]byte(salt)] = key
+	}
+	reader := newDecryptingReader(r, key)
+	_, err := io.Copy(w, reader)
+	return err
+}
+
+func Decrypt(w io.Writer, r io.Reader, password string, pwCache PasswordCache) error {
+	bufReader := bufio.NewReaderSize(r, 1)
+	b, err := bufReader.Peek(1)
+	if err != nil {
+		if err == io.EOF {
+			return fmt.Errorf("no input")
+		}
+		return err
+	}
+	if b[0] == 0 {
+		return decryptBinary(w, bufReader, password, pwCache)
+	}
+	if b[0] != '-' {
+		return errors.New("invalid input")
+	}
+	return decryptBinary(w, base64.NewDecoder(base64.StdEncoding, &lineReader{r: *bufio.NewScanner(bufReader)}), password, pwCache)
+}
+
+func DecryptFile(fileName, password string, pwCache PasswordCache) (err error) {
+	var outFileName string
+	if name, ok := strings.CutSuffix(fileName, ".enc"); ok {
+		outFileName = name
+	} else if name, ok := strings.CutSuffix(fileName, ".enc.txt"); ok {
+		outFileName = name
+	} else {
+		outFileName = fileName + ".dec"
+	}
+	fIn, err := os.Open(fileName)
+	if err != nil {
+		return err
+	}
+	defer fIn.Close()
+	fOut, err := os.Create(outFileName)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		fOut.Close()
+		if err != nil {
+			os.Remove(fOut.Name())
+		}
+	}()
+	if err := Decrypt(fOut, fIn, password, pwCache); err != nil {
+		return err
+	}
+	return fOut.Close()
+}
diff --git a/internal/sym/enc.go b/internal/sym/enc.go
new file mode 100644
index 0000000..32ec307
--- /dev/null
+++ b/internal/sym/enc.go
@@ -0,0 +1,102 @@
+package sym
+
+import (
+	"bufio"
+	"encoding/base64"
+	"encoding/binary"
+	"io"
+	"os"
+)
+
+type newlineWriter struct {
+	w *bufio.Writer
+	n int
+}
+
+func (w *newlineWriter) Write(buf []byte) (int, error) {
+	const lineSize = 80
+	nn := 0
+	for len(buf) > 0 {
+		if w.n == lineSize {
+			if err := w.w.WriteByte('\n'); err != nil {
+				return nn, err
+			}
+			w.n = 0
+		}
+		n, err := w.w.Write(buf[:min(lineSize-w.n, len(buf))])
+		nn += n
+		buf = buf[n:]
+		w.n += n
+		if err != nil {
+			return nn, err
+		}
+	}
+	return nn, nil
+}
+
+func Encrypt(w io.Writer, r io.Reader, key, salt []byte, counter int) error {
+	if _, err := w.Write([]byte{0}); err != nil {
+		return err
+	}
+	if _, err := w.Write(salt); err != nil {
+		return err
+	}
+	var noncePrefix [noncePrefixSize]byte
+	binary.BigEndian.PutUint32(noncePrefix[:], uint32(counter))
+	writer := newEncryptingWriter(w, key, noncePrefix)
+	if _, err := io.Copy(writer, r); err != nil {
+		return err
+	}
+	return writer.Close()
+}
+
+func EncryptBase64(w io.Writer, r io.Reader, key, salt []byte, count int) error {
+	bufWriter := bufio.NewWriter(w)
+	if _, err := bufWriter.WriteString(`-------------------------- Begin encrypted text block --------------------------
+-------------------------- am i cool like gpg? ---------------------------------
+`); err != nil {
+		return err
+	}
+	base64Writer := base64.NewEncoder(base64.StdEncoding, &newlineWriter{w: bufWriter})
+	if err := Encrypt(base64Writer, r, key, salt, count); err != nil {
+		return err
+	}
+	if err := base64Writer.Close(); err != nil {
+		return err
+	}
+	if err := bufWriter.WriteByte('\n'); err != nil {
+		return err
+	}
+	return bufWriter.Flush()
+}
+
+func EncryptFile(fileName string, key, salt []byte, count int, asciiOutput bool) (err error) {
+	f, err := os.Open(fileName)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	ext := ".enc"
+	if asciiOutput {
+		ext = ".enc.txt"
+	}
+	fOut, err := os.Create(fileName + ext)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		fOut.Close()
+		if err != nil {
+			os.Remove(fOut.Name())
+		}
+	}()
+	if asciiOutput {
+		err = EncryptBase64(fOut, f, key, salt, count)
+	} else {
+		err = Encrypt(fOut, f, key, salt, count)
+	}
+	if err != nil {
+		return err
+	}
+	return fOut.Close()
+}
diff --git a/internal/sym/oae.go b/internal/sym/oae.go
new file mode 100644
index 0000000..e71d5c3
--- /dev/null
+++ b/internal/sym/oae.go
@@ -0,0 +1,203 @@
+package sym
+
+import (
+	"bufio"
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"encoding/binary"
+	"errors"
+	"io"
+	"math"
+)
+
+const (
+	nonceSize       = 12
+	aeadOverhead    = 16
+	noncePrefixSize = nonceSize - 8
+
+	segmentSize          = 4 * 1024 * 1024
+	encryptedSegmentSize = segmentSize + aeadOverhead
+)
+
+type segmentEncrypter struct {
+	key         []byte
+	noncePrefix [noncePrefixSize]byte
+
+	aead cipher.AEAD
+	i    uint64
+}
+
+func (se *segmentEncrypter) initialize() error {
+	block, err := aes.NewCipher(se.key)
+	if err != nil {
+		return err
+	}
+	se.aead, err = cipher.NewGCM(block)
+	return err
+}
+
+func (se *segmentEncrypter) nonce(lastSegment bool) ([]byte, []byte, error) {
+	if se.i == math.MaxUint64 {
+		return nil, nil, errors.New("counter overflowed")
+	}
+	nonce := make([]byte, nonceSize)
+	copy(nonce, se.noncePrefix[:])
+	binary.BigEndian.PutUint64(nonce[noncePrefixSize:], se.i)
+	ad := make([]byte, 9)
+	binary.BigEndian.PutUint64(ad, se.i)
+	if lastSegment {
+		ad[8] = 1
+	}
+	se.i++
+	return nonce, ad, nil
+}
+
+func (se *segmentEncrypter) encrypt(out, buf []byte, lastSegment bool) ([]byte, error) {
+	nonce, ad, err := se.nonce(lastSegment)
+	if err != nil {
+		return nil, err
+	}
+	return se.aead.Seal(out, nonce, buf, ad), nil
+}
+
+func (se *segmentEncrypter) decrypt(out, buf []byte, lastSegment bool) ([]byte, error) {
+	nonce, ad, err := se.nonce(lastSegment)
+	if err != nil {
+		return nil, err
+	}
+	return se.aead.Open(out, nonce, buf, ad)
+}
+
+type encryptingWriter struct {
+	w           io.Writer
+	encrypter   segmentEncrypter
+	buf         []byte
+	initialized bool
+}
+
+func newEncryptingWriter(w io.Writer, key []byte, noncePrefix [noncePrefixSize]byte) *encryptingWriter {
+	return &encryptingWriter{
+		w: w,
+		encrypter: segmentEncrypter{
+			key:         key,
+			noncePrefix: noncePrefix,
+		},
+	}
+}
+
+func (w *encryptingWriter) initialize() error {
+	if w.initialized {
+		return nil
+	}
+	if err := w.encrypter.initialize(); err != nil {
+		return err
+	}
+	if _, err := w.w.Write(w.encrypter.noncePrefix[:]); err != nil {
+		return err
+	}
+	w.buf = make([]byte, 0, encryptedSegmentSize)
+	w.initialized = true
+	return nil
+}
+
+func (w *encryptingWriter) writeBuf(lastSegment bool) error {
+	var err error
+	if w.buf, err = w.encrypter.encrypt(w.buf[:0], w.buf, lastSegment); err != nil {
+		return err
+	}
+	if _, err := w.w.Write(w.buf); err != nil {
+		return err
+	}
+	w.buf = w.buf[:0]
+	return nil
+}
+
+func (w *encryptingWriter) Write(buf []byte) (int, error) {
+	if err := w.initialize(); err != nil {
+		return 0, err
+	}
+	nn := 0
+	for len(buf) > 0 {
+		if len(w.buf) == segmentSize {
+			if err := w.writeBuf(false); err != nil {
+				return nn, err
+			}
+		}
+		n := copy(w.buf[len(w.buf):segmentSize], buf)
+		nn += n
+		w.buf = w.buf[:len(w.buf)+n]
+		buf = buf[n:]
+	}
+	return nn, nil
+}
+
+func (w *encryptingWriter) Close() error {
+	if err := w.initialize(); err != nil {
+		return err
+	}
+	return w.writeBuf(true)
+}
+
+type decryptingReader struct {
+	r           *bufio.Reader
+	decrypter   segmentEncrypter
+	buf         bytes.Buffer
+	initialized bool
+}
+
+func newDecryptingReader(r io.Reader, key []byte) *decryptingReader {
+	return &decryptingReader{
+		r: bufio.NewReaderSize(r, 1),
+		decrypter: segmentEncrypter{
+			key: key,
+		},
+	}
+}
+
+func (r *decryptingReader) initialize() error {
+	if r.initialized {
+		return nil
+	}
+	if _, err := io.ReadFull(r.r, r.decrypter.noncePrefix[:]); err != nil {
+		return err
+	}
+	if err := r.decrypter.initialize(); err != nil {
+		return err
+	}
+	r.buf = *bytes.NewBuffer(make([]byte, 0, encryptedSegmentSize))
+	r.initialized = true
+	return nil
+}
+
+func (r *decryptingReader) fillBuf() error {
+	r.buf.Reset()
+	buf := r.buf.AvailableBuffer()[:encryptedSegmentSize]
+	n, err := io.ReadFull(r.r, buf)
+	if n == 0 {
+		if err == io.ErrUnexpectedEOF {
+			return io.EOF
+		}
+		return err
+	}
+	buf = buf[:n]
+	_, readErr := r.r.Peek(1)
+	buf, err = r.decrypter.decrypt(buf[:0], buf, readErr == io.EOF)
+	if err != nil {
+		return err
+	}
+	r.buf.Write(buf)
+	return nil
+}
+
+func (r *decryptingReader) Read(buf []byte) (int, error) {
+	if err := r.initialize(); err != nil {
+		return 0, err
+	}
+	if r.buf.Len() == 0 {
+		if err := r.fillBuf(); err != nil {
+			return 0, err
+		}
+	}
+	return r.buf.Read(buf)
+}
diff --git a/internal/sym/pwhash.go b/internal/sym/pwhash.go
new file mode 100644
index 0000000..ef17182
--- /dev/null
+++ b/internal/sym/pwhash.go
@@ -0,0 +1,12 @@
+package sym
+
+import (
+	"crypto/pbkdf2"
+	"crypto/sha256"
+)
+
+const SaltSize = 16
+
+func HashPassword(password string, salt []byte) ([]byte, error) {
+	return pbkdf2.Key(sha256.New, password, salt, 35_000_000, 32)
+}
diff --git a/internal/sym/sym_test.go b/internal/sym/sym_test.go
new file mode 100644
index 0000000..0ab0144
--- /dev/null
+++ b/internal/sym/sym_test.go
@@ -0,0 +1,69 @@
+package sym
+
+import (
+	"bytes"
+	"encoding/hex"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func mustHex(t *testing.T, s string) []byte {
+	t.Helper()
+	b, err := hex.DecodeString(s)
+	if err != nil {
+		t.Fatalf("Bad hex %q: %s", s, err)
+	}
+	return b
+}
+
+func TestEncryptDecrypt(t *testing.T) {
+	t.Parallel()
+
+	const password = "karp cache tidal mars fed rajah uses graze pobox flew"
+	salt := mustHex(t, "9aa7d8bb6d19f794162f4062c789b230")
+	key, err := HashPassword(password, salt)
+	if err != nil {
+		t.Fatalf("HashPassword failed: %s", err)
+	}
+	buf := make([]byte, 10*1024*1024)
+	for i := range buf {
+		buf[i] = byte(i)
+	}
+	for _, tc := range []struct {
+		desc  string
+		ascii bool
+	}{{
+		desc:  "binary",
+		ascii: false,
+	}, {
+		desc:  "ascii",
+		ascii: true,
+	}} {
+		t.Run(tc.desc, func(t *testing.T) {
+			t.Parallel()
+
+			fileName := filepath.Join(t.TempDir(), "file")
+			if err := os.WriteFile(fileName, buf, 0600); err != nil {
+				t.Fatalf("Failed to write test file: %s", err)
+			}
+			if err := EncryptFile(fileName, key, salt, 0, tc.ascii); err != nil {
+				t.Fatalf("EncryptFile failed: %s", err)
+			}
+			ext := ".enc"
+			if tc.ascii {
+				ext = ".enc.txt"
+			}
+			if err := DecryptFile(fileName+ext, password, make(PasswordCache)); err != nil {
+				t.Fatalf("DecryptFile failed: %s", err)
+			}
+			gotContents, err := os.ReadFile(fileName)
+			if err != nil {
+				t.Fatalf("Failed to read file: %s", err)
+			}
+			if !bytes.Equal(gotContents, buf) {
+				t.Errorf("contents differ")
+			}
+		})
+	}
+}
-- 
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