From 60cfb19d9068e50179a9ebfd3838c13647aeaa89 Mon Sep 17 00:00:00 2001
From: "F. Duncanh" <fduncanh@gmail.com>
Date: Thu, 23 Nov 2023 20:31:23 -0500
Subject: [PATCH] crypto.c: add AES GCM 128 en/decryption

---
 lib/crypto.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/crypto.h | 11 ++++++-
 2 files changed, 91 insertions(+), 1 deletion(-)

diff --git a/lib/crypto.c b/lib/crypto.c
index dc140e4..09344ad 100644
--- a/lib/crypto.c
+++ b/lib/crypto.c
@@ -262,6 +262,87 @@ void x25519_derive_secret(unsigned char secret[X25519_KEY_SIZE], const x25519_ke
     EVP_PKEY_CTX_free(pctx);
 }
 
+// GCM AES 128
+
+int gcm_encrypt(const unsigned char *plaintext, int plaintext_len, unsigned char *ciphertext,
+                unsigned char *key, unsigned char *iv, unsigned char *tag)
+{
+    EVP_CIPHER_CTX *ctx;
+
+    int len;
+    
+    int ciphertext_len;
+
+    if(!(ctx = EVP_CIPHER_CTX_new()))
+      handle_error(__func__);
+
+    if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_128_gcm(), NULL, NULL, NULL))
+        handle_error(__func__);
+
+    if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
+        handle_error(__func__);
+
+    if(1 != EVP_EncryptInit_ex(ctx, NULL, NULL, key, iv))
+        handle_error(__func__);
+
+    if(1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
+        handle_error(__func__);
+    ciphertext_len = len;
+
+    if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len))
+        handle_error(__func__);
+    ciphertext_len += len;
+
+    if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, tag))
+        handle_error(__func__);
+
+    EVP_CIPHER_CTX_free(ctx);
+
+    return ciphertext_len;
+}
+
+int gcm_decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *plaintext,
+                unsigned char *key, unsigned char *iv, unsigned char *tag)
+{
+    EVP_CIPHER_CTX *ctx;
+    int len;
+    int plaintext_len;
+    int ret;
+    
+    if(!(ctx = EVP_CIPHER_CTX_new()))
+        handle_error(__func__);
+
+    if(!EVP_DecryptInit_ex(ctx, EVP_aes_128_gcm(), NULL, NULL, NULL))
+        handle_error(__func__);
+
+    if(!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
+        handle_error(__func__);
+
+    if(!EVP_DecryptInit_ex(ctx, NULL, NULL, key, iv))
+        handle_error(__func__);
+
+    if(!EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
+        handle_error(__func__);
+    plaintext_len = len;
+
+    if(!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, 16, tag))
+        handle_error(__func__);
+
+    ret = EVP_DecryptFinal_ex(ctx, plaintext + len, &len);
+
+    EVP_CIPHER_CTX_free(ctx);
+    
+    if(ret > 0) {
+        /* Success */
+        plaintext_len += len;
+        return plaintext_len;
+    } else {
+        /* Verify failed */
+	printf("failed\n");
+        return -1;
+    }
+}
+
 // ED25519
 
 struct ed25519_key_s {
diff --git a/lib/crypto.h b/lib/crypto.h
index 13c5f28..d00b3dd 100644
--- a/lib/crypto.h
+++ b/lib/crypto.h
@@ -16,6 +16,8 @@
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
+ *
+ *  modified by fduncanh 2023
  */
 
 /*
@@ -64,9 +66,16 @@ x25519_key_t *x25519_key_generate(void);
 x25519_key_t *x25519_key_from_raw(const unsigned char data[X25519_KEY_SIZE]);
 void x25519_key_get_raw(unsigned char data[X25519_KEY_SIZE], const x25519_key_t *key);
 void x25519_key_destroy(x25519_key_t *key);
-
+int get_random_bytes(unsigned char *buf, int num);
+  
 void x25519_derive_secret(unsigned char secret[X25519_KEY_SIZE], const x25519_key_t *ours, const x25519_key_t *theirs);
 
+// GCM AES 128
+
+int gcm_encrypt(const unsigned char *plaintext, int plaintext_len, unsigned char *ciphertext,
+                unsigned char *key, unsigned char *iv, unsigned char *tag);
+int gcm_decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *plaintext,
+                unsigned char *key, unsigned char *iv, unsigned char *tag);
 // ED25519
 
 #define ED25519_KEY_SIZE 32