summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
Diffstat
-rw-r--r--internal/stupidgcm/stupidgcm.go184
-rw-r--r--internal/stupidgcm/stupidgcm_test.go154
2 files changed, 338 insertions, 0 deletions
diff --git a/internal/stupidgcm/stupidgcm.go b/internal/stupidgcm/stupidgcm.go
new file mode 100644
index 0000000..6773a35
--- /dev/null
+++ b/internal/stupidgcm/stupidgcm.go
@@ -0,0 +1,184 @@
+// Package stupidgcm is a thin wrapper for OpenSSL's GCM encryption and
+// decryption functions. It only support 32-byte keys and 16-bit IVs.
+package stupidgcm
+
+// #include <openssl/evp.h>
+// #cgo pkg-config: libcrypto
+import "C"
+
+import (
+ "fmt"
+ "log"
+ "unsafe"
+)
+
+const (
+ keyLen = 32
+ ivLen = 16
+ tagLen = 16
+)
+
+// stupidGCM implements the cipher.AEAD interface
+type stupidGCM struct {
+ key []byte
+}
+
+func New(key []byte) stupidGCM {
+ if len(key) != keyLen {
+ log.Panicf("Only %d-byte keys are supported", keyLen)
+ }
+ return stupidGCM{key: key}
+}
+
+func (g stupidGCM) NonceSize() int {
+ return ivLen
+}
+
+func (g stupidGCM) Overhead() int {
+ return tagLen
+}
+
+// Seal - encrypt "in" using "iv" and "authData" and append the result to "dst"
+func (g stupidGCM) Seal(dst, iv, in, authData []byte) []byte {
+ if len(iv) != ivLen {
+ log.Panicf("Only %d-byte IVs are supported", ivLen)
+ }
+ if len(in) == 0 {
+ log.Panic("Zero-length input data is not supported")
+ }
+ buf := make([]byte, len(in)+tagLen)
+
+ // https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
+
+ // Create scratch space "context"
+ ctx := C.EVP_CIPHER_CTX_new()
+ if ctx == nil {
+ log.Panic("EVP_CIPHER_CTX_new failed")
+ }
+
+ // Set cipher to AES-256
+ if C.EVP_EncryptInit_ex(ctx, C.EVP_aes_256_gcm(), nil, nil, nil) != 1 {
+ log.Panic("EVP_EncryptInit_ex I failed")
+ }
+
+ // Use 16-byte IV
+ if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_SET_IVLEN, ivLen, nil) != 1 {
+ log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_GCM_SET_IVLEN failed")
+ }
+
+ // Set key and IV
+ if C.EVP_EncryptInit_ex(ctx, nil, nil, (*C.uchar)(&g.key[0]), (*C.uchar)(&iv[0])) != 1 {
+ log.Panic("EVP_EncryptInit_ex II failed")
+ }
+
+ // Provide authentication data
+ var resultLen C.int
+ if C.EVP_EncryptUpdate(ctx, nil, &resultLen, (*C.uchar)(&authData[0]), C.int(len(authData))) != 1 {
+ log.Panic("EVP_EncryptUpdate authData failed")
+ }
+ if int(resultLen) != len(authData) {
+ log.Panicf("Unexpected length %d", resultLen)
+ }
+
+ // Encrypt "in" into "buf"
+ if C.EVP_EncryptUpdate(ctx, (*C.uchar)(&buf[0]), &resultLen, (*C.uchar)(&in[0]), C.int(len(in))) != 1 {
+ log.Panic("EVP_EncryptUpdate failed")
+ }
+ if int(resultLen) != len(in) {
+ log.Panicf("Unexpected length %d", resultLen)
+ }
+
+ // Finalise encryption
+ // Because GCM is a stream encryption, this will not write out any data.
+ dummy := make([]byte, 16)
+ if C.EVP_EncryptFinal_ex(ctx, (*C.uchar)(&dummy[0]), &resultLen) != 1 {
+ log.Panic("EVP_EncryptFinal_ex failed")
+ }
+ if resultLen != 0 {
+ log.Panicf("Unexpected length %d", resultLen)
+ }
+
+ // Get GMAC tag and append it to the ciphertext in "buf"
+ if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_GET_TAG, tagLen, (unsafe.Pointer)(&buf[len(in)])) != 1 {
+ log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_GCM_GET_TAG failed")
+ }
+
+ // Free scratch space
+ C.EVP_CIPHER_CTX_free(ctx)
+
+ return append(dst, buf...)
+}
+
+// Open - decrypt "in" using "iv" and "authData" and append the result to "dst"
+func (g stupidGCM) Open(dst, iv, in, authData []byte) ([]byte, error) {
+ if len(iv) != ivLen {
+ log.Panicf("Only %d-byte IVs are supported", ivLen)
+ }
+ if len(in) <= tagLen {
+ log.Panic("Input data too short")
+ }
+ buf := make([]byte, len(in)-tagLen)
+ ciphertext := in[:len(in)-tagLen]
+ tag := in[len(in)-tagLen:]
+
+ // https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
+
+ // Create scratch space "context"
+ ctx := C.EVP_CIPHER_CTX_new()
+ if ctx == nil {
+ log.Panic("EVP_CIPHER_CTX_new failed")
+ }
+
+ // Set cipher to AES-256
+ if C.EVP_DecryptInit_ex(ctx, C.EVP_aes_256_gcm(), nil, nil, nil) != 1 {
+ log.Panic("EVP_DecryptInit_ex I failed")
+ }
+
+ // Use 16-byte IV
+ if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_SET_IVLEN, ivLen, nil) != 1 {
+ log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_GCM_SET_IVLEN failed")
+ }
+
+ // Set key and IV
+ if C.EVP_DecryptInit_ex(ctx, nil, nil, (*C.uchar)(&g.key[0]), (*C.uchar)(&iv[0])) != 1 {
+ log.Panic("EVP_DecryptInit_ex II failed")
+ }
+
+ // Provide authentication data
+ var resultLen C.int
+ if C.EVP_DecryptUpdate(ctx, nil, &resultLen, (*C.uchar)(&authData[0]), C.int(len(authData))) != 1 {
+ log.Panic("EVP_EncryptUpdate authData failed")
+ }
+ if int(resultLen) != len(authData) {
+ log.Panicf("Unexpected length %d", resultLen)
+ }
+
+ // Decrypt "ciphertext" into "buf"
+ if C.EVP_DecryptUpdate(ctx, (*C.uchar)(&buf[0]), &resultLen, (*C.uchar)(&ciphertext[0]), C.int(len(ciphertext))) != 1 {
+ log.Panic("EVP_DecryptUpdate failed")
+ }
+ if int(resultLen) != len(ciphertext) {
+ log.Panicf("Unexpected length %d", resultLen)
+ }
+
+ // Set expected GMAC tag
+ if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_SET_TAG, tagLen, (unsafe.Pointer)(&tag[0])) != 1 {
+ log.Panic("EVP_CIPHER_CTX_ctrl failed")
+ }
+
+ // Check GMAC
+ dummy := make([]byte, 16)
+ res := C.EVP_DecryptFinal_ex(ctx, (*C.uchar)(&dummy[0]), &resultLen)
+ if resultLen != 0 {
+ log.Panicf("Unexpected length %d", resultLen)
+ }
+
+ // Free scratch space
+ C.EVP_CIPHER_CTX_free(ctx)
+
+ if res != 1 {
+ return nil, fmt.Errorf("stupidgcm: message authentication failed")
+ }
+
+ return append(dst, buf...), nil
+}
diff --git a/internal/stupidgcm/stupidgcm_test.go b/internal/stupidgcm/stupidgcm_test.go
new file mode 100644
index 0000000..dfd495d
--- /dev/null
+++ b/internal/stupidgcm/stupidgcm_test.go
@@ -0,0 +1,154 @@
+package stupidgcm
+
+import (
+ "bytes"
+ "crypto/aes"
+ "crypto/cipher"
+ "crypto/rand"
+ "encoding/hex"
+ "testing"
+)
+
+// Get "n" random bytes from /dev/urandom or panic
+func randBytes(n int) []byte {
+ b := make([]byte, n)
+ _, err := rand.Read(b)
+ if err != nil {
+ panic("Failed to read random bytes: " + err.Error())
+ }
+ return b
+}
+
+// TestEncryptDecrypt encrypts and decrypts using both stupidgcm and Go's built-in
+// GCM implemenatation and verifies that the results are identical.
+func TestEncryptDecrypt(t *testing.T) {
+ key := randBytes(32)
+ sGCM := New(key)
+ authData := randBytes(24)
+ iv := randBytes(16)
+ dst := make([]byte, 71) // 71 = random length
+
+ gAES, err := aes.NewCipher(key)
+ if err != nil {
+ t.Fatal(err)
+ }
+ gGCM, err := cipher.NewGCMWithNonceSize(gAES, 16)
+ if err != nil {
+ t.Fatal(err)
+ }
+
+ // Check all block sizes from 1 to 5000
+ for i := 1; i < 5000; i++ {
+ in := make([]byte, i)
+
+ sOut := sGCM.Seal(dst, iv, in, authData)
+ gOut := gGCM.Seal(dst, iv, in, authData)
+
+ // Ciphertext must be identical to Go GCM
+ if bytes.Compare(sOut, gOut) != 0 {
+ t.Fatalf("Compare failed for encryption, size %d", i)
+ t.Log("sOut:")
+ t.Log("\n" + hex.Dump(sOut))
+ t.Log("gOut:")
+ t.Log("\n" + hex.Dump(gOut))
+ }
+
+ sOut2, sErr := sGCM.Open(dst, iv, sOut[len(dst):], authData)
+ if sErr != nil {
+ t.Fatal(sErr)
+ }
+ gOut2, gErr := gGCM.Open(dst, iv, gOut[len(dst):], authData)
+ if gErr != nil {
+ t.Fatal(gErr)
+ }
+
+ // Plaintext must be identical to Go GCM
+ if bytes.Compare(sOut2, gOut2) != 0 {
+ t.Fatalf("Compare failed for decryption, size %d", i)
+ }
+ }
+}
+
+// TestCorruption verifies that changes in the ciphertext result in a decryption
+// error
+func TestCorruption(t *testing.T) {
+ key := randBytes(32)
+ sGCM := New(key)
+ authData := randBytes(24)
+ iv := randBytes(16)
+
+ in := make([]byte, 354)
+ sOut := sGCM.Seal(nil, iv, in, authData)
+ sOut2, sErr := sGCM.Open(nil, iv, sOut, authData)
+ if sErr != nil {
+ t.Fatal(sErr)
+ }
+ if bytes.Compare(in, sOut2) != 0 {
+ t.Fatalf("Compare failed")
+ }
+
+ // Corrupt first byte
+ sOut[0]++
+ sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
+ if sErr == nil || sOut2 != nil {
+ t.Fatalf("Should have gotten error")
+ }
+ sOut[0]--
+
+ // Corrupt last byte
+ sOut[len(sOut)-1]++
+ sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
+ if sErr == nil || sOut2 != nil {
+ t.Fatalf("Should have gotten error")
+ }
+ sOut[len(sOut)-1]--
+
+ // Append one byte
+ sOut = append(sOut, 0)
+ sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
+ if sErr == nil || sOut2 != nil {
+ t.Fatalf("Should have gotten error")
+ }
+}
+
+// $ go test -bench .
+// PASS
+// Benchmark4kEncStupidGCM-2 50000 25622 ns/op 159.86 MB/s
+// Benchmark4kEncGoGCM-2 10000 116544 ns/op 35.15 MB/s
+// ok github.com/rfjakob/gocryptfs/internal/stupidgcm 3.775s
+func Benchmark4kEncStupidGCM(b *testing.B) {
+ key := randBytes(32)
+ authData := randBytes(24)
+ iv := randBytes(16)
+ in := make([]byte, 4096)
+ b.SetBytes(int64(len(in)))
+
+ sGCM := New(key)
+
+ for i := 0; i < b.N; i++ {
+ // Encrypt and append to nonce
+ sGCM.Seal(iv, iv, in, authData)
+ }
+}
+
+func Benchmark4kEncGoGCM(b *testing.B) {
+ key := randBytes(32)
+ authData := randBytes(24)
+ iv := randBytes(16)
+ in := make([]byte, 4096)
+ b.SetBytes(int64(len(in)))
+
+ gAES, err := aes.NewCipher(key)
+ if err != nil {
+ b.Fatal(err)
+ }
+ gGCM, err := cipher.NewGCMWithNonceSize(gAES, 16)
+ if err != nil {
+ b.Fatal(err)
+ }
+
+ for i := 0; i < b.N; i++ {
+ // Encrypt and append to nonce
+ gGCM.Seal(iv, iv, in, authData)
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2025-10-31 16:13:29 +0000