stupidgcm: add chacha20poly1305 via openssl

"stupidChacha20poly1305".

XChaCha will build upon this.

2 files changed, 393 insertions, 0 deletions

diff --git a/internal/stupidgcm/stupidchacha.go b/internal/stupidgcm/stupidchacha.go
new file mode 100644
index 0000000..e2f6407
--- /dev/null
+++ b/internal/stupidgcm/stupidchacha.go
@@ -0,0 +1,222 @@
+// +build !without_openssl
+
+package stupidgcm
+
+// #include <openssl/evp.h>
+// #cgo pkg-config: libcrypto
+import "C"
+
+import (
+	"crypto/cipher"
+	"fmt"
+	"log"
+	"unsafe"
+
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+type stupidChacha20poly1305 struct {
+	key []byte
+}
+
+// Verify that we satisfy the cipher.AEAD interface
+var _ cipher.AEAD = &stupidChacha20poly1305{}
+
+func newChacha20poly1305(keyIn []byte) cipher.AEAD {
+	if len(keyIn) != chacha20poly1305.KeySize {
+		log.Panicf("Only %d-byte keys are supported, you passed %d bytes", chacha20poly1305.KeySize, len(keyIn))
+	}
+	// Create a private copy of the key
+	key := append([]byte{}, keyIn...)
+	return &stupidChacha20poly1305{key: key}
+}
+
+// NonceSize returns the required size of the nonce / IV.
+func (g *stupidChacha20poly1305) NonceSize() int {
+	return chacha20poly1305.NonceSize
+}
+
+// Overhead returns the number of bytes that are added for authentication.
+func (g *stupidChacha20poly1305) Overhead() int {
+	return tagLen
+}
+
+// Seal encrypts "in" using "iv" and "authData" and append the result to "dst"
+func (g *stupidChacha20poly1305) Seal(dst, iv, in, authData []byte) []byte {
+	if len(iv) != g.NonceSize() {
+		log.Panicf("Only %d-byte IVs are supported, you passed %d bytes", g.NonceSize(), len(iv))
+	}
+	if len(in) == 0 {
+		log.Panic("Zero-length input data is not supported")
+	}
+	if len(g.key) != chacha20poly1305.KeySize {
+		log.Panicf("Wrong key length: %d. Key has been wiped?", len(g.key))
+	}
+
+	// If the "dst" slice is large enough we can use it as our output buffer
+	outLen := len(in) + tagLen
+	var buf []byte
+	inplace := false
+	if cap(dst)-len(dst) >= outLen {
+		inplace = true
+		buf = dst[len(dst) : len(dst)+outLen]
+	} else {
+		buf = make([]byte, outLen)
+	}
+
+	// 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
+	if C.EVP_EncryptInit_ex(ctx, C.EVP_chacha20_poly1305(), nil, nil, nil) != 1 {
+		log.Panic("EVP_EncryptInit_ex I 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 MAC tag and append it to the ciphertext in "buf"
+	if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_AEAD_GET_TAG, tagLen, (unsafe.Pointer)(&buf[len(in)])) != 1 {
+		log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_AEAD_GET_TAG failed")
+	}
+
+	// Free scratch space
+	C.EVP_CIPHER_CTX_free(ctx)
+
+	if inplace {
+		return dst[:len(dst)+outLen]
+	}
+	return append(dst, buf...)
+}
+
+// Open decrypts "in" using "iv" and "authData" and append the result to "dst"
+func (g *stupidChacha20poly1305) Open(dst, iv, in, authData []byte) ([]byte, error) {
+	if len(iv) != g.NonceSize() {
+		log.Panicf("Only %d-byte IVs are supported", g.NonceSize())
+	}
+	if len(g.key) != chacha20poly1305.KeySize {
+		log.Panicf("Wrong key length: %d. Key has been wiped?", len(g.key))
+	}
+	if len(in) <= tagLen {
+		return nil, fmt.Errorf("stupidChacha20poly1305: input data too short (%d bytes)", len(in))
+	}
+
+	// If the "dst" slice is large enough we can use it as our output buffer
+	outLen := len(in) - tagLen
+	var buf []byte
+	inplace := false
+	if cap(dst)-len(dst) >= outLen {
+		inplace = true
+		buf = dst[len(dst) : len(dst)+outLen]
+	} else {
+		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_chacha20_poly1305(), nil, nil, nil) != 1 {
+		log.Panic("EVP_DecryptInit_ex I 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")
+	}
+
+	// Set expected MAC tag
+	if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_AEAD_SET_TAG, tagLen, (unsafe.Pointer)(&tag[0])) != 1 {
+		log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_AEAD_SET_TAG 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_DecryptUpdate 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)
+	}
+
+	// Check MAC
+	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, ErrAuth
+	}
+
+	if inplace {
+		return dst[:len(dst)+outLen], nil
+	}
+	return append(dst, buf...), nil
+}
+
+// Wipe tries to wipe the AES key from memory by overwriting it with zeros
+// and setting the reference to nil.
+//
+// This is not bulletproof due to possible GC copies, but
+// still raises to bar for extracting the key.
+func (g *stupidChacha20poly1305) Wipe() {
+	for i := range g.key {
+		g.key[i] = 0
+	}
+	g.key = nil
+}
diff --git a/internal/stupidgcm/stupidchacha_test.go b/internal/stupidgcm/stupidchacha_test.go
new file mode 100644
index 0000000..010055f
--- /dev/null
+++ b/internal/stupidgcm/stupidchacha_test.go
@@ -0,0 +1,171 @@
+// +build !without_openssl
+
+// We compare against Go's built-in GCM implementation. Since stupidgcm only
+// supports 128-bit IVs and Go only supports that from 1.5 onward, we cannot
+// run these tests on older Go versions.
+package stupidgcm
+
+import (
+	"bytes"
+	"encoding/hex"
+	"testing"
+
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+// TestEncryptDecrypt encrypts and decrypts using both stupidgcm and Go's built-in
+// GCM implementation and verifies that the results are identical.
+func TestEncryptDecryptChacha(t *testing.T) {
+	key := randBytes(32)
+	sGCM := newChacha20poly1305(key)
+	authData := randBytes(24)
+	iv := randBytes(sGCM.NonceSize())
+	dst := make([]byte, 71) // 71 = random length
+
+	gGCM, err := chacha20poly1305.New(key)
+	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.Equal(sOut, gOut) {
+			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.Equal(sOut2, gOut2) {
+			t.Fatalf("Compare failed for decryption, size %d", i)
+		}
+	}
+}
+
+// Seal re-uses the "dst" buffer it is large enough.
+// Check that this works correctly by testing different "dst" capacities from
+// 5000 to 16 and "in" lengths from 1 to 5000.
+func TestInplaceSealChacha(t *testing.T) {
+	key := randBytes(32)
+	sGCM := newChacha20poly1305(key)
+	authData := randBytes(24)
+	iv := randBytes(sGCM.NonceSize())
+
+	gGCM, err := chacha20poly1305.New(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	max := 5016
+	// Check all block sizes from 1 to 5000
+	for i := 1; i < max-len(iv); i++ {
+		in := make([]byte, i)
+		dst := make([]byte, max-i)
+		dst = dst[:len(iv)]
+
+		sOut := sGCM.Seal(dst, iv, in, authData)
+		dst2 := make([]byte, len(iv))
+		gOut := gGCM.Seal(dst2, iv, in, authData)
+
+		// Ciphertext must be identical to Go GCM
+		if !bytes.Equal(sOut, gOut) {
+			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))
+		}
+	}
+}
+
+// Open re-uses the "dst" buffer it is large enough.
+// Check that this works correctly by testing different "dst" capacities from
+// 5000 to 16 and "in" lengths from 1 to 5000.
+func TestInplaceOpenChacha(t *testing.T) {
+	key := randBytes(32)
+	sGCM := newChacha20poly1305(key)
+	authData := randBytes(24)
+	iv := randBytes(sGCM.NonceSize())
+
+	gGCM, err := chacha20poly1305.New(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	max := 5016
+	// Check all block sizes from 1 to 5000
+	for i := 1; i < max-len(iv); i++ {
+		in := make([]byte, i)
+
+		gCiphertext := gGCM.Seal(iv, iv, in, authData)
+
+		dst := make([]byte, max-i)
+		// sPlaintext ... stupidgcm plaintext
+		sPlaintext, err := sGCM.Open(dst[:0], iv, gCiphertext[len(iv):], authData)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Plaintext must be identical to Go GCM
+		if !bytes.Equal(in, sPlaintext) {
+			t.Fatalf("Compare failed, i=%d", i)
+		}
+	}
+}
+
+// TestCorruption verifies that changes in the ciphertext result in a decryption
+// error
+func TestCorruptionChacha(t *testing.T) {
+	key := randBytes(32)
+	sGCM := newChacha20poly1305(key)
+	authData := randBytes(24)
+	iv := randBytes(sGCM.NonceSize())
+
+	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.Equal(in, sOut2) {
+		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")
+	}
+}