// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library fuchsia.drm;

/// The maximum size of an `EncryptionScheme` string.
const MAX_ENCRYPTION_SCHEME_SIZE uint32 = 4;

/// The maximum size of a `EncryptionKeyId` blob.
const MAX_KEY_ID_SIZE uint32 = 16;

/// The maximum size of a `EncryptionInitVector` blob.
const MAX_INIT_VECTOR_SIZE uint32 = 16;

/// Identifies an encryption scheme.
// TODO(dalesat): Should this use a flexible enum?
alias EncryptionScheme = string:MAX_ENCRYPTION_SCHEME_SIZE;
const ENCRYPTION_SCHEME_CENC string = "cenc";
const ENCRYPTION_SCHEME_CBC1 string = "cbc1";
const ENCRYPTION_SCHEME_CENS string = "cens";
const ENCRYPTION_SCHEME_CBCS string = "cbcs";
alias EncryptionKeyId = vector<uint8>:MAX_KEY_ID_SIZE;
alias EncryptionInitVector = vector<uint8>:MAX_INIT_VECTOR_SIZE;

/// A byte range within a sample consisting of a clear byte range
/// followed by an encrypted byte range. This structure specifies the size of
/// each range in the subsample.
type EncryptionSubsampleEntry = struct {
    clear_bytes uint32;
    encrypted_bytes uint32;
};

/// Pattern encryption utilizes a pattern of encrypted and clear 16 byte blocks
/// over the protected range of a subsample (the encrypted_bytes of a
/// `SubsampleEntry`). This structure specifies the number of encrypted data
/// blocks followed by the number of clear data blocks.
type EncryptionPattern = struct {
    clear_blocks uint32;
    encrypted_blocks uint32;
};

/// The stream format details payload of a decrypting stream processor. This is
/// a sparsely populated table to specify parameters necessary for decryption
/// other than the data stream. It is only necessary to update fields if they
/// changed, but not an error if the same value is repeated.
// TODO(dalesat): Why are fields below prefixed with 'default_'?
type Encryption = table {
    /// Specifies which encryption scheme to use, such as `ENCRYPTION_SCHEME_CENC`.
    /// Usage:
    ///  - It is required to be set prior to delivery of input packets.
    ///  - Changing the scheme mid-stream is only permitted in some scenarios.
    ///    Once an encrypted scheme is selected for a stream, the scheme may
    ///    only be set to `ENCRYPTION_SCHEME_UNENCRYPTED` or that
    ///    same initial encrypted scheme. The scheme may be set to
    ///    `ENCRYPTION_SCHEME_UNENCRYPTED` at any point.
    1: scheme EncryptionScheme;

    /// Identifies the key that should be used for decrypting subsequent data.
    /// Usage:
    ///  - It is required to be set prior to delivery of input packets to a
    ///    decryptor.
    ///  - This may be changed multiple times during a data stream.
    2: default_key_id EncryptionKeyId;

    /// Used in combination with a key and a block of content
    /// to create the first cipher block in a chain and derive subsequent cipher
    /// blocks in a cipher block chain.
    /// Usage:
    ///  - It is required to be set prior to the delivery of input packets to a
    ///    decryptor.
    ///  - This may be changed multiple times during a data stream.
    3: default_init_vector EncryptionInitVector;

    /// Used to identify the clear and encrypted blocks for pattern based encryption.
    /// Usage:
    /// - This is not allowed for CENC and CBC1 and required for CENS and CBCS.
    /// - If required, it must be set prior to the delivery of input packets to
    ///   a decryptor.
    /// - This may be changed multiple times during a data stream.
    4: default_pattern EncryptionPattern;
};