allow building on default os x

since it doesn't have gcm stuff put it in a conditionally built
file.

Change-Id: I8083ff9b86b6fe0723fd21ffc77038b7679c97c7

ciphers_gcm.go

@@ -0,0 +1,141 @@
+// Copyright (C) 2014 Space Monkey, Inc.
+// +build cgo,!darwin
+
+package openssl
+
+// #include <openssl/evp.h>
+import "C"
+
+import (
+	"errors"
+	"fmt"
+)
+
+type AuthenticatedEncryptionCipherCtx interface {
+	EncryptionCipherCtx
+
+	// data passed in to ExtraData() is part of the final output; it is
+	// not encrypted itself, but is part of the authenticated data. when
+	// decrypting or authenticating, pass back with the decryption
+	// context's ExtraData()
+	ExtraData([]byte) error
+
+	// use after finalizing encryption to get the authenticating tag
+	GetTag() ([]byte, error)
+}
+
+type AuthenticatedDecryptionCipherCtx interface {
+	DecryptionCipherCtx
+
+	// pass in any extra data that was added during encryption with the
+	// encryption context's ExtraData()
+	ExtraData([]byte) error
+
+	// use before finalizing decryption to tell the library what the
+	// tag is expected to be
+	SetTag([]byte) error
+}
+
+type authEncryptionCipherCtx struct {
+	*encryptionCipherCtx
+}
+
+type authDecryptionCipherCtx struct {
+	*decryptionCipherCtx
+}
+
+func getGCMCipher(blocksize int) (*Cipher, error) {
+	var cipherptr *C.EVP_CIPHER
+	switch blocksize {
+	case 256:
+		cipherptr = C.EVP_aes_256_gcm()
+	case 192:
+		cipherptr = C.EVP_aes_192_gcm()
+	case 128:
+		cipherptr = C.EVP_aes_128_gcm()
+	default:
+		return nil, fmt.Errorf("unknown block size %d", blocksize)
+	}
+	return &Cipher{ptr: cipherptr}, nil
+}
+
+func NewGCMEncryptionCipherCtx(blocksize int, e *Engine, key, iv []byte) (
+	AuthenticatedEncryptionCipherCtx, error) {
+	cipher, err := getGCMCipher(blocksize)
+	if err != nil {
+		return nil, err
+	}
+	ctx, err := newEncryptionCipherCtx(cipher, e, key, nil)
+	if err != nil {
+		return nil, err
+	}
+	if iv != nil {
+		err := ctx.setCtrl(C.EVP_CTRL_GCM_SET_IVLEN, len(iv))
+		if err != nil {
+			return nil, fmt.Errorf("could not set IV len to %d: %s",
+				len(iv), err)
+		}
+		if 1 != C.EVP_EncryptInit_ex(ctx.ctx, nil, nil, nil,
+			(*C.uchar)(&iv[0])) {
+			return nil, errors.New("failed to apply IV")
+		}
+	}
+	return &authEncryptionCipherCtx{encryptionCipherCtx: ctx}, nil
+}
+
+func NewGCMDecryptionCipherCtx(blocksize int, e *Engine, key, iv []byte) (
+	AuthenticatedDecryptionCipherCtx, error) {
+	cipher, err := getGCMCipher(blocksize)
+	if err != nil {
+		return nil, err
+	}
+	ctx, err := newDecryptionCipherCtx(cipher, e, key, nil)
+	if err != nil {
+		return nil, err
+	}
+	if iv != nil {
+		err := ctx.setCtrl(C.EVP_CTRL_GCM_SET_IVLEN, len(iv))
+		if err != nil {
+			return nil, fmt.Errorf("could not set IV len to %d: %s",
+				len(iv), err)
+		}
+		if 1 != C.EVP_DecryptInit_ex(ctx.ctx, nil, nil, nil,
+			(*C.uchar)(&iv[0])) {
+			return nil, errors.New("failed to apply IV")
+		}
+	}
+	return &authDecryptionCipherCtx{decryptionCipherCtx: ctx}, nil
+}
+
+func (ctx *authEncryptionCipherCtx) ExtraData(aad []byte) error {
+	if aad == nil {
+		return nil
+	}
+	var outlen C.int
+	if 1 != C.EVP_EncryptUpdate(ctx.ctx, nil, &outlen, (*C.uchar)(&aad[0]),
+		C.int(len(aad))) {
+		return errors.New("failed to add additional authenticated data")
+	}
+	return nil
+}
+
+func (ctx *authDecryptionCipherCtx) ExtraData(aad []byte) error {
+	if aad == nil {
+		return nil
+	}
+	var outlen C.int
+	if 1 != C.EVP_DecryptUpdate(ctx.ctx, nil, &outlen, (*C.uchar)(&aad[0]),
+		C.int(len(aad))) {
+		return errors.New("failed to add additional authenticated data")
+	}
+	return nil
+}
+
+func (ctx *authEncryptionCipherCtx) GetTag() ([]byte, error) {
+	return ctx.getCtrlBytes(C.EVP_CTRL_GCM_GET_TAG, GCM_TAG_MAXLEN,
+		GCM_TAG_MAXLEN)
+}
+
+func (ctx *authDecryptionCipherCtx) SetTag(tag []byte) error {
+	return ctx.setCtrlBytes(C.EVP_CTRL_GCM_SET_TAG, len(tag), tag)
+}