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authorJakob Unterwurzacher2016-05-01 22:26:47 +0200
committerJakob Unterwurzacher2016-05-04 19:56:07 +0200
commitc92190bf07d27a4c7fbecba5778d11c77c52574e (patch)
tree0e6cfeaeb2580d3b20e90d056881432b7f61a293 /internal/stupidgcm/stupidgcm.go
parent1bb907b38e1fefdfb4ad66f1d423a607477deb3c (diff)
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 )
Diffstat (limited to 'internal/stupidgcm/stupidgcm.go')
-rw-r--r--internal/stupidgcm/stupidgcm.go184
1 files changed, 184 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
+}