MDEV-8022 Assertion `rc == 0' failed in ma_encrypt on dropping an encrypted Aria table

fix encryption of the last partial block

* now really encrypt it, using key and iv
* support the case of very short plaintext (less than one block)
* recommend aes_ctr over aes_cbc, because the former
  doesn't have problems with partial blocks

mysql-test/suite/encryption/r/aria_tiny.result

+set global aria_encrypt_tables = 1;
+create table t1 (i int, key(i)) engine=aria;
+insert into t1 values (1);
+drop table t1;
+set global aria_encrypt_tables = 0;

mysql-test/suite/encryption/t/aria_tiny.test

+#
+# MDEV-8022 Assertion `rc == 0' failed in ma_encrypt on dropping an encrypted Aria table
+#
+
+--source include/have_file_key_management_plugin.inc
+
+set global aria_encrypt_tables = 1;
+create table t1 (i int, key(i)) engine=aria;
+insert into t1 values (1);
+drop table t1;
+set global aria_encrypt_tables = 0;
+

mysys_ssl/my_crypt.cc

@@ -71,6 +71,10 @@ static int block_crypt(CipherMode cipher, Dir dir,
 {
   int tail= source_length % MY_AES_BLOCK_SIZE;
 
+  DBUG_ASSERT(source_length);
+
+  if (likely(source_length >= MY_AES_BLOCK_SIZE || !no_padding))
+  {
 #ifdef HAVE_YASSL
     TaoCrypt::AES ctx(dir, cipher);
 
@@ -81,7 +85,7 @@ static int block_crypt(CipherMode cipher, Dir dir,
     if (iv)
     {
       ctx.SetIV(iv);
-    DBUG_ASSERT(TaoCrypt::AES::BLOCK_SIZE == iv_length);
+      DBUG_ASSERT(TaoCrypt::AES::BLOCK_SIZE <= iv_length);
     }
     DBUG_ASSERT(TaoCrypt::AES::BLOCK_SIZE == MY_AES_BLOCK_SIZE);
 
@@ -121,7 +125,7 @@ static int block_crypt(CipherMode cipher, Dir dir,
     EVP_CIPHER_CTX_set_padding(&ctx, !no_padding);
 
     DBUG_ASSERT(EVP_CIPHER_CTX_key_length(&ctx) == (int)key_length);
-  DBUG_ASSERT(EVP_CIPHER_CTX_iv_length(&ctx) == (int)iv_length);
+    DBUG_ASSERT(EVP_CIPHER_CTX_iv_length(&ctx) <= (int)iv_length);
     DBUG_ASSERT(EVP_CIPHER_CTX_block_size(&ctx) == MY_AES_BLOCK_SIZE);
 
     /* use built-in OpenSSL padding, if possible */
@@ -133,22 +137,28 @@ static int block_crypt(CipherMode cipher, Dir dir,
     *dest_length += fin;
 
 #endif
+  }
 
   if (no_padding && tail)
   {
     /*
       Not much we can do, block ciphers cannot encrypt data that aren't
       a multiple of the block length. At least not without padding.
-      What we do here, we XOR the tail with the previous encrypted block.
+      Let's do something CTR-like for the last partial block.
     */
 
-    if (unlikely(source_length < MY_AES_BLOCK_SIZE))
-      return MY_AES_BAD_DATA;
+    uchar mask[MY_AES_BLOCK_SIZE];
+    uint mlen;
+
+    DBUG_ASSERT(iv_length >= sizeof(mask));
+    my_aes_encrypt_ecb(iv, sizeof(mask), mask, &mlen,
+                       key, key_length, 0, 0, 1);
+    DBUG_ASSERT(mlen == sizeof(mask));
 
     const uchar *s= source + source_length - tail;
     const uchar *e= source + source_length;
     uchar *d= dest + source_length - tail;
-    const uchar *m= (dir == CRYPT_ENCRYPT ? d : s) - MY_AES_BLOCK_SIZE;
+    const uchar *m= mask;
     while (s < e)
       *d++ = *s++ ^ *m++;
     *dest_length= source_length;
@@ -204,7 +214,7 @@ int my_aes_encrypt_ecb(const uchar* source, uint source_length,
                        int no_padding)
 {
   return block_crypt(aes_ecb(key_length), CRYPT_ENCRYPT, source, source_length,
-                     dest, dest_length, key, key_length, 0, 0, no_padding);
+                     dest, dest_length, key, key_length, iv, iv_length, no_padding);
 }
 
 int my_aes_decrypt_ecb(const uchar* source, uint source_length,
@@ -214,7 +224,7 @@ int my_aes_decrypt_ecb(const uchar* source, uint source_length,
                        int no_padding)
 {
   return block_crypt(aes_ecb(key_length), CRYPT_DECRYPT, source, source_length,
-                     dest, dest_length, key, key_length, 0, 0, no_padding);
+                     dest, dest_length, key, key_length, iv, iv_length, no_padding);
 }
 
 int my_aes_encrypt_cbc(const uchar* source, uint source_length,

plugin/file_key_management/file_key_management_plugin.cc

@@ -50,7 +50,7 @@ static MYSQL_SYSVAR_STR(filekey, filekey,
 
 static MYSQL_SYSVAR_ENUM(encryption_algorithm, encryption_algorithm,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
-  "Encryption algorithm to use.",
+  "Encryption algorithm to use, aes_ctr is the recommended one.",
   NULL, NULL, 0, &encryption_algorithm_typelib);
 
 static struct st_mysql_sys_var* settings[] = {