aws_encryption_sdk.internal.utils

Helper utility functions for AWS Encryption SDK.

Functions

content_type(frame_length)	Returns the appropriate content type based on the frame length.
get_aad_content_string(content_type, ...)	Prepares the appropriate Body AAD Value for a message body.
message_id(size)	Generates a new message ID.
prep_stream_data(data)	Take an input and prepare it for use as a stream.
prepare_data_keys(primary_master_key, ...)	Prepares a DataKey to be used for encrypting message and list of EncryptedDataKey objects to be serialized into header.
source_data_key_length_check(...)	Validates that the supplied source_data_key's data_key is the correct length for the supplied algorithm's kdf_input_len value.
validate_frame_length(frame_length, algorithm)	Validates that frame length is within the defined limits and is compatible with the selected algorithm.

aws_encryption_sdk.internal.utils.content_type(frame_length)

Returns the appropriate content type based on the frame length.

Parameters

frame_length (int) – Message frame length

Returns

Appropriate content type based on frame length

Return type

aws_encryption_sdk.identifiers.ContentType

aws_encryption_sdk.internal.utils.validate_frame_length(frame_length, algorithm)

Validates that frame length is within the defined limits and is compatible with the selected algorithm.

Parameters

• frame_length (int) – Frame size in bytes

• algorithm (aws_encryption_sdk.identifiers.Algorithm) – Algorithm to use for encryption

Raises

• SerializationError – if frame size is negative or not a multiple of the algorithm block size

• SerializationError – if frame size is larger than the maximum allowed frame size

aws_encryption_sdk.internal.utils.message_id(size)

Generates a new message ID.

Parameters

size (int) – The size of the message id to generate, in bytes

Returns

Message ID

Return type

bytes

aws_encryption_sdk.internal.utils.get_aad_content_string(content_type, is_final_frame)

Prepares the appropriate Body AAD Value for a message body.

Parameters

• content_type (aws_encryption_sdk.identifiers.ContentType) – Defines the type of content for which to prepare AAD String

• is_final_frame (bool) – Boolean stating whether this is the final frame in a body

Returns

Appropriate AAD Content String

Return type

bytes

Raises

UnknownIdentityError – if unknown content type

aws_encryption_sdk.internal.utils.prepare_data_keys(primary_master_key, master_keys, algorithm, encryption_context)

Prepares a DataKey to be used for encrypting message and list of EncryptedDataKey objects to be serialized into header.

Parameters

• primary_master_key (aws_encryption_sdk.key_providers.base.MasterKey) – Master key with which to generate the encryption data key

• master_keys (list of aws_encryption_sdk.key_providers.base.MasterKey) – All master keys with which to encrypt data keys

• algorithm (aws_encryption_sdk.identifiers.Algorithm) – Algorithm to use for encryption

• encryption_context (dict) – Encryption context to use when generating data key

Return type

tuple containing aws_encryption_sdk.structures.DataKey and set of aws_encryption_sdk.structures.EncryptedDataKey

aws_encryption_sdk.internal.utils.prep_stream_data(data)

Take an input and prepare it for use as a stream.

Parameters

data – Input data

Returns

Prepared stream

Return type

InsistentReaderBytesIO

aws_encryption_sdk.internal.utils.source_data_key_length_check(source_data_key, algorithm)

Validates that the supplied source_data_key’s data_key is the correct length for the supplied algorithm’s kdf_input_len value.

Parameters

• source_data_key (aws_encryption_sdk.structures.RawDataKey or aws_encryption_sdk.structures.DataKey) – Source data key object received from MasterKey decrypt or generate data_key methods

• algorithm (aws_encryption_sdk.identifiers.Algorithm) – Algorithm object which directs how this data key will be used

Raises

InvalidDataKeyError – if data key length does not match required kdf input length