Get off of deprecated GCM AES methods

Multiple compiler warnings note that the gcm_aes_* family of functions are deprecated. They have been replaced with gcm_aes<key_length>_*. This change uses the correct set of functions based on the given key size. Resolves #571.

Sample compiler warning:

/home/noviv/opendht/src/crypto.cpp: In function ‘dht::Blob dht::crypto::aesEncrypt(const uint8_t*, size_t, const dht::Blob&)’:
/home/noviv/opendht/src/crypto.cpp:97:20: warning: ‘void nettle_gcm_aes_set_key(gcm_aes_ctx*, size_t, const uint8_t*)’ is deprecated [-Wdeprecated-declarations]
   97 |     gcm_aes_set_key(&aes, key.size(), key.data());
         |                    ^
         In file included from /home/noviv/opendht/src/crypto.cpp:27:
         /usr/include/nettle/gcm.h:276:1: note: declared here
           276 | gcm_aes_set_key(struct gcm_aes_ctx *ctx,
                 | ^~~~~~~~~~~~~~~)

gnutls/nettle@6a19845 marked the functions as deprecated.

src/crypto.cpp

@@ -93,11 +93,27 @@ Blob aesEncrypt(const uint8_t* data, size_t data_length, const Blob& key)
         std::random_device rdev;
         std::generate_n(ret.begin(), GCM_IV_SIZE, std::bind(rand_byte, std::ref(rdev)));
     }
-    struct gcm_aes_ctx aes;
-    gcm_aes_set_key(&aes, key.size(), key.data());
-    gcm_aes_set_iv(&aes, GCM_IV_SIZE, ret.data());
-    gcm_aes_encrypt(&aes, data_length, ret.data() + GCM_IV_SIZE, data);
-    gcm_aes_digest(&aes, GCM_DIGEST_SIZE, ret.data() + GCM_IV_SIZE + data_length);
+
+    if (key.size() == AES_LENGTHS[0]) {
+        struct gcm_aes128_ctx aes;
+        gcm_aes128_set_key(&aes, key.data());
+        gcm_aes128_set_iv(&aes, GCM_IV_SIZE, ret.data());
+        gcm_aes128_encrypt(&aes, data_length, ret.data() + GCM_IV_SIZE, data);
+        gcm_aes128_digest(&aes, GCM_DIGEST_SIZE, ret.data() + GCM_IV_SIZE + data_length);
+    } else if (key.size() == AES_LENGTHS[1]) {
+        struct gcm_aes192_ctx aes;
+        gcm_aes192_set_key(&aes, key.data());
+        gcm_aes192_set_iv(&aes, GCM_IV_SIZE, ret.data());
+        gcm_aes192_encrypt(&aes, data_length, ret.data() + GCM_IV_SIZE, data);
+        gcm_aes192_digest(&aes, GCM_DIGEST_SIZE, ret.data() + GCM_IV_SIZE + data_length);
+    } else if (key.size() == AES_LENGTHS[2]) {
+        struct gcm_aes256_ctx aes;
+        gcm_aes256_set_key(&aes, key.data());
+        gcm_aes256_set_iv(&aes, GCM_IV_SIZE, ret.data());
+        gcm_aes256_encrypt(&aes, data_length, ret.data() + GCM_IV_SIZE, data);
+        gcm_aes256_digest(&aes, GCM_DIGEST_SIZE, ret.data() + GCM_IV_SIZE + data_length);
+    }
+
     return ret;
 }
 
@@ -118,14 +134,28 @@ Blob aesDecrypt(const uint8_t* data, size_t data_length, const Blob& key)
 
     std::array<uint8_t, GCM_DIGEST_SIZE> digest;
 
-    struct gcm_aes_ctx aes;
-    gcm_aes_set_key(&aes, key.size(), key.data());
-    gcm_aes_set_iv(&aes, GCM_IV_SIZE, data);
-
     size_t data_sz = data_length - GCM_IV_SIZE - GCM_DIGEST_SIZE;
     Blob ret(data_sz);
-    gcm_aes_decrypt(&aes, data_sz, ret.data(), data + GCM_IV_SIZE);
-    gcm_aes_digest(&aes, GCM_DIGEST_SIZE, digest.data());
+
+    if (key.size() == AES_LENGTHS[0]) {
+        struct gcm_aes128_ctx aes;
+        gcm_aes128_set_key(&aes, key.data());
+        gcm_aes128_set_iv(&aes, GCM_IV_SIZE, data);
+        gcm_aes128_decrypt(&aes, data_sz, ret.data(), data + GCM_IV_SIZE);
+        gcm_aes128_digest(&aes, GCM_DIGEST_SIZE, digest.data());
+    } else if (key.size() == AES_LENGTHS[1]) {
+        struct gcm_aes192_ctx aes;
+        gcm_aes192_set_key(&aes, key.data());
+        gcm_aes192_set_iv(&aes, GCM_IV_SIZE, data);
+        gcm_aes192_decrypt(&aes, data_sz, ret.data(), data + GCM_IV_SIZE);
+        gcm_aes192_digest(&aes, GCM_DIGEST_SIZE, digest.data());
+    } else if (key.size() == AES_LENGTHS[2]) {
+        struct gcm_aes256_ctx aes;
+        gcm_aes256_set_key(&aes, key.data());
+        gcm_aes256_set_iv(&aes, GCM_IV_SIZE, data);
+        gcm_aes256_decrypt(&aes, data_sz, ret.data(), data + GCM_IV_SIZE);
+        gcm_aes256_digest(&aes, GCM_DIGEST_SIZE, digest.data());
+    }
 
     if (not std::equal(digest.begin(), digest.end(), data + data_length - GCM_DIGEST_SIZE)) {
         throw DecryptError("Can't decrypt data");