stupidgcm: add our own thin wrapper around openssl gcm
...complete with tests and benchmark. This will allow us to get rid of the dependency to spacemonkeygo/openssl that causes problems on Arch Linux ( https://github.com/rfjakob/gocryptfs/issues/21 )
This commit is contained in:
Jakob Unterwurzacher
parent
1bb907b38e
commit
c92190bf07
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// Package stupidgcm is a thin wrapper for OpenSSL's GCM encryption and
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// decryption functions. It only support 32-byte keys and 16-bit IVs.
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package stupidgcm
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// #include <openssl/evp.h>
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// #cgo pkg-config: libcrypto
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import "C"
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import (
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"fmt"
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"log"
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"unsafe"
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)
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const (
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keyLen = 32
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ivLen = 16
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tagLen = 16
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)
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// stupidGCM implements the cipher.AEAD interface
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type stupidGCM struct {
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key []byte
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}
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func New(key []byte) stupidGCM {
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if len(key) != keyLen {
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log.Panicf("Only %d-byte keys are supported", keyLen)
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}
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return stupidGCM{key: key}
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}
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func (g stupidGCM) NonceSize() int {
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return ivLen
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}
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func (g stupidGCM) Overhead() int {
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return tagLen
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}
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// Seal - encrypt "in" using "iv" and "authData" and append the result to "dst"
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func (g stupidGCM) Seal(dst, iv, in, authData []byte) []byte {
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if len(iv) != ivLen {
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log.Panicf("Only %d-byte IVs are supported", ivLen)
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}
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if len(in) == 0 {
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log.Panic("Zero-length input data is not supported")
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}
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buf := make([]byte, len(in)+tagLen)
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// https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
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// Create scratch space "context"
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ctx := C.EVP_CIPHER_CTX_new()
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if ctx == nil {
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log.Panic("EVP_CIPHER_CTX_new failed")
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}
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// Set cipher to AES-256
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if C.EVP_EncryptInit_ex(ctx, C.EVP_aes_256_gcm(), nil, nil, nil) != 1 {
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log.Panic("EVP_EncryptInit_ex I failed")
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}
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// Use 16-byte IV
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if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_SET_IVLEN, ivLen, nil) != 1 {
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log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_GCM_SET_IVLEN failed")
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}
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// Set key and IV
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if C.EVP_EncryptInit_ex(ctx, nil, nil, (*C.uchar)(&g.key[0]), (*C.uchar)(&iv[0])) != 1 {
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log.Panic("EVP_EncryptInit_ex II failed")
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}
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// Provide authentication data
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var resultLen C.int
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if C.EVP_EncryptUpdate(ctx, nil, &resultLen, (*C.uchar)(&authData[0]), C.int(len(authData))) != 1 {
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log.Panic("EVP_EncryptUpdate authData failed")
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}
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if int(resultLen) != len(authData) {
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log.Panicf("Unexpected length %d", resultLen)
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}
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// Encrypt "in" into "buf"
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if C.EVP_EncryptUpdate(ctx, (*C.uchar)(&buf[0]), &resultLen, (*C.uchar)(&in[0]), C.int(len(in))) != 1 {
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log.Panic("EVP_EncryptUpdate failed")
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}
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if int(resultLen) != len(in) {
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log.Panicf("Unexpected length %d", resultLen)
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}
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// Finalise encryption
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// Because GCM is a stream encryption, this will not write out any data.
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dummy := make([]byte, 16)
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if C.EVP_EncryptFinal_ex(ctx, (*C.uchar)(&dummy[0]), &resultLen) != 1 {
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log.Panic("EVP_EncryptFinal_ex failed")
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}
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if resultLen != 0 {
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log.Panicf("Unexpected length %d", resultLen)
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}
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// Get GMAC tag and append it to the ciphertext in "buf"
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if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_GET_TAG, tagLen, (unsafe.Pointer)(&buf[len(in)])) != 1 {
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log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_GCM_GET_TAG failed")
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}
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// Free scratch space
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C.EVP_CIPHER_CTX_free(ctx)
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return append(dst, buf...)
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}
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// Open - decrypt "in" using "iv" and "authData" and append the result to "dst"
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func (g stupidGCM) Open(dst, iv, in, authData []byte) ([]byte, error) {
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if len(iv) != ivLen {
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log.Panicf("Only %d-byte IVs are supported", ivLen)
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}
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if len(in) <= tagLen {
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log.Panic("Input data too short")
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}
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buf := make([]byte, len(in)-tagLen)
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ciphertext := in[:len(in)-tagLen]
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tag := in[len(in)-tagLen:]
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// https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
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// Create scratch space "context"
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ctx := C.EVP_CIPHER_CTX_new()
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if ctx == nil {
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log.Panic("EVP_CIPHER_CTX_new failed")
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}
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// Set cipher to AES-256
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if C.EVP_DecryptInit_ex(ctx, C.EVP_aes_256_gcm(), nil, nil, nil) != 1 {
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log.Panic("EVP_DecryptInit_ex I failed")
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}
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// Use 16-byte IV
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if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_SET_IVLEN, ivLen, nil) != 1 {
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log.Panic("EVP_CIPHER_CTX_ctrl EVP_CTRL_GCM_SET_IVLEN failed")
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}
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// Set key and IV
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if C.EVP_DecryptInit_ex(ctx, nil, nil, (*C.uchar)(&g.key[0]), (*C.uchar)(&iv[0])) != 1 {
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log.Panic("EVP_DecryptInit_ex II failed")
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}
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// Provide authentication data
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var resultLen C.int
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if C.EVP_DecryptUpdate(ctx, nil, &resultLen, (*C.uchar)(&authData[0]), C.int(len(authData))) != 1 {
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log.Panic("EVP_EncryptUpdate authData failed")
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}
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if int(resultLen) != len(authData) {
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log.Panicf("Unexpected length %d", resultLen)
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}
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// Decrypt "ciphertext" into "buf"
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if C.EVP_DecryptUpdate(ctx, (*C.uchar)(&buf[0]), &resultLen, (*C.uchar)(&ciphertext[0]), C.int(len(ciphertext))) != 1 {
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log.Panic("EVP_DecryptUpdate failed")
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}
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if int(resultLen) != len(ciphertext) {
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log.Panicf("Unexpected length %d", resultLen)
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}
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// Set expected GMAC tag
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if C.EVP_CIPHER_CTX_ctrl(ctx, C.EVP_CTRL_GCM_SET_TAG, tagLen, (unsafe.Pointer)(&tag[0])) != 1 {
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log.Panic("EVP_CIPHER_CTX_ctrl failed")
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}
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// Check GMAC
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dummy := make([]byte, 16)
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res := C.EVP_DecryptFinal_ex(ctx, (*C.uchar)(&dummy[0]), &resultLen)
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if resultLen != 0 {
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log.Panicf("Unexpected length %d", resultLen)
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}
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// Free scratch space
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C.EVP_CIPHER_CTX_free(ctx)
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if res != 1 {
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return nil, fmt.Errorf("stupidgcm: message authentication failed")
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}
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return append(dst, buf...), nil
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}
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@ -0,0 +1,154 @@
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package stupidgcm
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import (
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"bytes"
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"encoding/hex"
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"testing"
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)
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// Get "n" random bytes from /dev/urandom or panic
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func randBytes(n int) []byte {
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b := make([]byte, n)
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_, err := rand.Read(b)
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if err != nil {
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panic("Failed to read random bytes: " + err.Error())
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}
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return b
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}
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// TestEncryptDecrypt encrypts and decrypts using both stupidgcm and Go's built-in
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// GCM implemenatation and verifies that the results are identical.
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func TestEncryptDecrypt(t *testing.T) {
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key := randBytes(32)
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sGCM := New(key)
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authData := randBytes(24)
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iv := randBytes(16)
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dst := make([]byte, 71) // 71 = random length
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gAES, err := aes.NewCipher(key)
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if err != nil {
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t.Fatal(err)
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}
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gGCM, err := cipher.NewGCMWithNonceSize(gAES, 16)
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if err != nil {
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t.Fatal(err)
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}
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// Check all block sizes from 1 to 5000
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for i := 1; i < 5000; i++ {
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in := make([]byte, i)
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sOut := sGCM.Seal(dst, iv, in, authData)
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gOut := gGCM.Seal(dst, iv, in, authData)
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// Ciphertext must be identical to Go GCM
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if bytes.Compare(sOut, gOut) != 0 {
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t.Fatalf("Compare failed for encryption, size %d", i)
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t.Log("sOut:")
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t.Log("\n" + hex.Dump(sOut))
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t.Log("gOut:")
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t.Log("\n" + hex.Dump(gOut))
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}
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sOut2, sErr := sGCM.Open(dst, iv, sOut[len(dst):], authData)
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if sErr != nil {
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t.Fatal(sErr)
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}
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gOut2, gErr := gGCM.Open(dst, iv, gOut[len(dst):], authData)
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if gErr != nil {
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t.Fatal(gErr)
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}
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// Plaintext must be identical to Go GCM
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if bytes.Compare(sOut2, gOut2) != 0 {
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t.Fatalf("Compare failed for decryption, size %d", i)
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}
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}
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}
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// TestCorruption verifies that changes in the ciphertext result in a decryption
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// error
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func TestCorruption(t *testing.T) {
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key := randBytes(32)
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sGCM := New(key)
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authData := randBytes(24)
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iv := randBytes(16)
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in := make([]byte, 354)
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sOut := sGCM.Seal(nil, iv, in, authData)
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sOut2, sErr := sGCM.Open(nil, iv, sOut, authData)
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if sErr != nil {
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t.Fatal(sErr)
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}
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if bytes.Compare(in, sOut2) != 0 {
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t.Fatalf("Compare failed")
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}
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// Corrupt first byte
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sOut[0]++
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sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
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if sErr == nil || sOut2 != nil {
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t.Fatalf("Should have gotten error")
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}
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sOut[0]--
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// Corrupt last byte
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sOut[len(sOut)-1]++
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sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
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if sErr == nil || sOut2 != nil {
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t.Fatalf("Should have gotten error")
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}
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sOut[len(sOut)-1]--
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// Append one byte
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sOut = append(sOut, 0)
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sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
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if sErr == nil || sOut2 != nil {
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t.Fatalf("Should have gotten error")
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}
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}
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// $ go test -bench .
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// PASS
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// Benchmark4kEncStupidGCM-2 50000 25622 ns/op 159.86 MB/s
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// Benchmark4kEncGoGCM-2 10000 116544 ns/op 35.15 MB/s
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// ok github.com/rfjakob/gocryptfs/internal/stupidgcm 3.775s
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func Benchmark4kEncStupidGCM(b *testing.B) {
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key := randBytes(32)
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authData := randBytes(24)
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iv := randBytes(16)
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in := make([]byte, 4096)
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b.SetBytes(int64(len(in)))
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sGCM := New(key)
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for i := 0; i < b.N; i++ {
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// Encrypt and append to nonce
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sGCM.Seal(iv, iv, in, authData)
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}
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}
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func Benchmark4kEncGoGCM(b *testing.B) {
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key := randBytes(32)
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authData := randBytes(24)
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iv := randBytes(16)
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in := make([]byte, 4096)
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b.SetBytes(int64(len(in)))
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gAES, err := aes.NewCipher(key)
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if err != nil {
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b.Fatal(err)
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}
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gGCM, err := cipher.NewGCMWithNonceSize(gAES, 16)
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if err != nil {
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b.Fatal(err)
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}
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for i := 0; i < b.N; i++ {
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// Encrypt and append to nonce
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gGCM.Seal(iv, iv, in, authData)
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}
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}
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