Handling substream dependencies in authenticating video data streams

An apparatus for encoding a video into a video data stream, wherein the apparatus is configured for rendering the video data stream checkable on trustworthiness in units of temporal segments of a sequence of temporal segments of the video data stream, wherein the apparatus is configured for

• acquiring a number of substreams of a predetermined temporal segment of the temporal segments, each of the substreams having a portion of the predetermined temporal segment associated therewith, the number of substreams having an order defined among them;
• acquiring dependency information, which indicates, for a substream of the number of substreams, whether the substream is independent or whether the substream depends on one or more reference substreams of the substream;
• rendering the substream of the predetermined temporal segment checkable on trustworthiness by
• using a hash function to derive a hash value based on the portion of the predetermined temporal segment which is associated with the substream;
• forming a verification string based on the hash value and based on a reference hash value by
• if the substream is independent, using, as the reference hash value, a hash value derived for the corresponding substream of the preceding temporal segment, the preceding temporal segment preceding the predetermined temporal segment in the sequence of temporal segments;
• and/or
• if the substream depends on one or more reference substreams out of the number of substreams, the reference hash value is based on one or more of the following
• if the predetermined temporal segment is the first temporal segment of the sequence of temporal segments, and/or if a preceding temporal segment, which directly precedes the predetermined temporal segment in the sequence of temporal segments is unverifiable, a bitstring of bits of a predetermined value, the bitstring comprising a predetermined length,
• a hash value derived for a predetermined substream of a preceding temporal segment, the preceding temporal segment preceding the predetermined temporal segment in the sequence of temporal segments, wherein the predetermined substream corresponds to one of the following:
• the lowest ranked substream within a set out of the one or more reference substreams,
• the highest ranked substream within a set out of the one or more reference substreams;
• acquiring a digital signature based on the verification string, and inserting an indication of the digital signature in the video data stream.

A method for decoding a video from a video data stream, wherein the method comprises checking the video data stream on trustworthiness in units of temporal segments of a sequence of temporal segments of the video data stream, wherein the method comprises:

• deriving a number of substreams of a predetermined temporal segment of the temporal segments, each of the substreams having a portion of the predetermined temporal segment associated therewith, the number of substreams having an order defined among them;
• deriving dependency information, which indicates, for a substream of the number of substreams, whether the substream is independent or whether the substream depends on one or more reference substreams of the substream;
• checking the substream of the predetermined temporal segment on trustworthiness by
• acquiring, based on an indication in the video data stream, a digital signature for the substream of the predetermined temporal segment,
• using a hash function to derive a hash value based on the portion of the predetermined temporal segment which is associated with the substream;
• forming a verification string based on the hash value and based on a reference hash value by
• if the substream is independent, using, as the reference hash value, a hash value derived for the corresponding substream of the preceding temporal segment, the preceding temporal segment preceding the predetermined temporal segment in the sequence of temporal segments;
• and/or
• if the substream depends on one or more reference substreams out of the number of substreams, the reference hash value is based on one or more of the following:
• if the predetermined temporal segment is the first temporal segment of the sequence of temporal segments, and/or if a preceding temporal segment, which directly precedes the predetermined temporal segment in the sequence of temporal segments is unverifiable, a bitstring of bits of a predetermined value, the bitstring comprising a predetermined length,
• a hash value derived for a predetermined substream;
• of a preceding temporal segment, the preceding temporal segment preceding the predetermined temporal segment in the sequence of temporal segments, wherein the predetermined substream corresponds to one of the following:
• the lowest ranked substream within a set out of the one or more reference substreams,
• the highest ranked substream within a set out of the one or more reference substreams;
• checking whether the verification string fits to the digital signature.

A non-transitory digital storage medium having stored thereon a video data stream comprising a video, wherein the video is encoded into the video data stream using a method for encoding a video into a video data stream, wherein the method comprises rendering the video data stream checkable on trustworthiness in units of temporal segments of a sequence of temporal segments of the video data stream, wherein the method comprises:

• acquiring a number of substreams of a predetermined temporal segment of the temporal segments, each of the substreams having a portion of the predetermined temporal segment associated therewith, the number of substreams having an order defined among them;
• acquiring dependency information, which indicates, for a substream of the number of substreams, whether the substream is independent or whether the substream depends on one or more reference substreams of the substream;
• rendering the substream of the predetermined temporal segment checkable on trustworthiness by
• using a hash function to derive a hash value based on the portion of the predetermined temporal segment which is associated with the substream;
• forming a verification string based on the hash value and based on a reference hash value by
• if the substream is independent, using, as the reference hash value, a hash value derived for the corresponding substream of the preceding temporal segment, the preceding temporal segment preceding the predetermined temporal segment in the sequence of temporal segments;
• and/or
• if the substream depends on one or more reference substreams out of the number of substreams, the reference hash value is based on one or more of the following
• if the predetermined temporal segment is the first temporal segment of the sequence of temporal segments, and/or if a preceding temporal segment, which directly precedes the predetermined temporal segment in the sequence of temporal segments is unverifiable, a bitstring of bits of a predetermined value, the bitstring comprising a predetermined length,
• a hash value derived for a predetermined substream of a preceding temporal segment, the preceding temporal segment preceding the predetermined temporal segment in the sequence of temporal segments, wherein the predetermined substream corresponds to one of the following:
• the lowest ranked substream within a set out of the one or more reference substreams,
• the highest ranked substream within a set out of the one or more reference substreams;
• acquiring a digital signature based on the verification string, and inserting an indication of the digital signature in the video data stream.