Move stream length check to try-catch

src/Telegram.Bot.Extensions.Passport/Decryption/Decrypter.cs

@@ -11,6 +11,9 @@
 // ReSharper disable once CheckNamespace
 namespace Telegram.Bot.Passport
 {
+    /// <summary>
+    /// Default implementation of <see cref="IDecrypter"/>
+    /// </summary>
     public class Decrypter : IDecrypter
     {
         /// <inheritdoc />
@@ -97,8 +100,6 @@ public Task DecryptFileAsync(
                 throw new ArgumentNullException(nameof(encryptedContent));
             if (fileCredentials is null)
                 throw new ArgumentNullException(nameof(fileCredentials));
-            if (encryptedContent.Length % 16 != 0)
-                throw new PassportDataDecryptionException($"Invalid data length: {encryptedContent.Length}");
             if (!destination.CanWrite)
                 throw new ArgumentException("Stream does not support writing.", nameof(destination));
 
@@ -143,45 +144,57 @@ CancellationToken cancellationToken
         {
             FindDataKeyAndIv(secret, hash, out byte[] dataKey, out byte[] dataIv);
 
-            using (var aes = Aes.Create())
+            try
             {
-                // ReSharper disable once PossibleNullReferenceException
-                aes.KeySize = 256;
-                aes.Mode = CipherMode.CBC;
-                aes.Key = dataKey;
-                aes.IV = dataIv;
-                aes.Padding = PaddingMode.None;
-
-                using (var decryptor = aes.CreateDecryptor())
-                using (CryptoStream aesStream = new CryptoStream(data, decryptor, CryptoStreamMode.Read))
-                using (var sha256 = SHA256.Create())
-                using (CryptoStream shaStream = new CryptoStream(aesStream, sha256, CryptoStreamMode.Read))
+                using (var aes = Aes.Create())
                 {
-                    byte[] paddingBuffer = new byte[256];
-                    int read = await shaStream.ReadAsync(paddingBuffer, 0, 256, cancellationToken)
-                        .ConfigureAwait(false);
-
-                    int paddingLength = paddingBuffer[0];
-                    if (paddingLength < 32)
-                        throw new PassportDataDecryptionException("Invalid padding size");
-
-                    if (read < paddingLength)
-                        throw new PassportDataDecryptionException("Invalid data");
-
-                    await destination.WriteAsync(paddingBuffer, paddingLength, read - paddingLength, cancellationToken)
-                        .ConfigureAwait(false);
-
-                    await shaStream.CopyToAsync(destination, 81920, cancellationToken)
-                        .ConfigureAwait(false);
+                    // ReSharper disable once PossibleNullReferenceException
+                    aes.KeySize = 256;
+                    aes.Mode = CipherMode.CBC;
+                    aes.Key = dataKey;
+                    aes.IV = dataIv;
+                    aes.Padding = PaddingMode.None;
 
-                    byte[] paddedDataHash = sha256.Hash;
-                    for (int i = 0; i < 32; i++)
+                    using (var decryptor = aes.CreateDecryptor())
+                    using (CryptoStream aesStream = new CryptoStream(data, decryptor, CryptoStreamMode.Read))
+                    using (var sha256 = SHA256.Create())
+                    using (CryptoStream shaStream = new CryptoStream(aesStream, sha256, CryptoStreamMode.Read))
                     {
-                        if (hash[i] != paddedDataHash[i])
-                            throw new PassportDataDecryptionException("Data hash mismatch");
+                        byte[] paddingBuffer = new byte[256];
+                        int read = await shaStream.ReadAsync(paddingBuffer, 0, 256, cancellationToken)
+                            .ConfigureAwait(false);
+
+                        int paddingLength = paddingBuffer[0];
+                        if (paddingLength < 32)
+                            throw new PassportDataDecryptionException("Invalid padding size");
+
+                        if (read < paddingLength)
+                            throw new PassportDataDecryptionException("Invalid data");
+
+                        await destination.WriteAsync(paddingBuffer, paddingLength, read - paddingLength, cancellationToken)
+                            .ConfigureAwait(false);
+
+                        // 81920 is the default Stream.CopyTo buffer size
+                        // The overload without the buffer size does not accept a cancellation token
+                        await shaStream.CopyToAsync(destination, 81920, cancellationToken)
+                            .ConfigureAwait(false);
+
+                        byte[] paddedDataHash = sha256.Hash;
+                        for (int i = 0; i < 32; i++)
+                        {
+                            if (hash[i] != paddedDataHash[i])
+                                throw new PassportDataDecryptionException("Data hash mismatch");
+                        }
                     }
                 }
             }
+            catch (CryptographicException ce)
+            when (ce.Message.Equals("The input data is not a complete block.", StringComparison.Ordinal))
+            {
+                // The length check in this case can not be performed before decryption
+                // since we could be dealing with a stream that does not support seeking
+                throw new PassportDataDecryptionException("Invalid data length");
+            }
         }
 
         private static byte[] DecryptDataBytes(byte[] data, byte[] secret, byte[] hash)
@@ -238,7 +251,7 @@ private static byte[] DecryptDataBytes(byte[] data, byte[] secret, byte[] hash)
 
             {
                 int paddingLength = dataWithPadding[0];
-                if (!(32 <= paddingLength && paddingLength < 256))
+                if (paddingLength < 32)
                 {
                     throw new PassportDataDecryptionException("Invalid data padding length");
                 }