Signing Video Data Using Salted Hash

Abstract

To provide a method and a device for signing video data using a mechanism that protects against a situation where an unpermitted party identifies a secret function used in a signing process on the basis of past signatures.SOLUTION: A method includes: obtaining video data representing a video sequence; obtaining a bit string not extracted from the video data; generating salt by hashing the bit string using a secret hash function; generating a first / second fingerprint by hashing a combination of the salt and a first / second portion of the video data or hashing a combination of the salt and a hash of the first / second portion of the video data; and providing a signature of the video data including the first fingerprint.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to the field of security measures for protecting programs or data from unauthorized actions. In particular, the present disclosure proposes a method and apparatus for signing video data. [Background technology]

[0002] In the field of secure digital communications, it is known to use so-called salts to prevent unauthorized parties from guessing repeatedly used passwords based on hashes of the password. Salts, sometimes called cryptographic salts, have also been used to prevent hash collisions, an abnormal condition in which hashing separate data items produces identical results. Hash collisions can disrupt internal system procedures and can also expose a system to attacks.

[0003] For example, US Patent No. 10,728,023 (B2) discloses a method for implementing a hash function with a content-based salt, which involves identifying a data block B of a given size, dividing this data block into x segments, and selecting y bytes from each of the segments to create a total of y total Byte and this y total performing a bitwise AND / OR operation on z bytes of the data block S(B) to obtain a salt for the data block S(B), computing a hash value h(B) of the data block, and computing a hash value h(h(B)*S(B)) of the concatenation of the hash value and the salt, which produces a unique fingerprint that can identify data block B, where the number of bytes selected y is a function of a number of calculations that is determined to avoid producing the same hash for two different data blocks.

[0004] CN113158248A discloses a method for securely storing video data, in which a data hash value is calculated for a combination of a data record, a timestamp, and an operation sequence number. A signature is generated from the hash value using a private key belonging to a key pair that also includes a public key. These elements are sent to a server, which stores the data record, timestamp, operation serial number, public key, and signature after successful verification.

[0005] US Patent Application Publication No. 20140010366(A1) discloses a method for cryptographic video verification in which the data of each video frame is extended with a timestamp before being hashed. The hash of the extended video frame is included in a cryptographically signed document.

[0006] WO0064094A1 discloses a method for inserting a digital signature into digital data, particularly video data. According to one disclosed embodiment, the digital signature is salted with a timestamp assigned by a trusted third party. The timestamp relates to the time of the timestamp and not to the time of acquisition of the digital data. In this embodiment, the digital data is hashed and signed, then combined with the timestamp, and the resulting combination is hashed and encrypted.

[0007] US Patent Application Publication No. 2011200224(A1) discloses a method for providing an identifier for a content item, the method including: generating a first identifier for the content item based at least in part on a baseband-level representation of the content item; generating a second identifier for the content item based at least in part on an encoded representation of the content item; and generating a message including the first identifier and the second identifier. The content item may be a video item, and the baseband-level representation includes raw video.

[0008] WO2017202451A1 discloses a method for providing secure electronic signatures by first sampling a biometric signature including time points and coordinates, then creating a set of polynomials based on the sampling. A hash calculation is then performed on the data to be signed, which is salted with data based on the polynomials from the sampling. Finally, the salted hash is encrypted with the private key from the restricted proof and stored with the signed data, hashing method, and public key to enable validation of the signature.

[0009] Available techniques for modifying hashes with content-based salts are not well suited for digitally signing video data, particularly data that encodes live video streams. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent No. 10728023(B2) [Patent Document 2] CN113158248A [Patent Document 3] U.S. Patent Application Publication No. 20140010366(A1) [Patent Document 4] WO0064094A1 [Patent Document 5] U.S. Patent Application Publication No. 2011200224(A1) [Patent Document 6] WO2017202451A1 [Non-patent literature]

[0011] [Non-Patent Document 1] Recommendation ITU-T H.264(06 / 2019) "Advanced video coding for generic audiovisual services" [Non-patent document 2] ITU-T H.265(08 / 2021) “High efficiency video coding” Summary of the Invention

[0012] One objective of the present disclosure is to create a usable method and apparatus for signing (digitally signing) video data using a mechanism that protects against an unauthorized party identifying the secret function used in the signing process based on a previous signature. This is particularly desirable when the secret function includes a hash function, given the limited number of available hash functions with proven capabilities to resist attacks. A further objective is to propose such a method and apparatus for generating digital signatures that can be verified in parallel with an ongoing process of continuously decoding a stream of video data, such as a live video stream. A specific objective is to propose a computationally efficient signing technique with these properties.

[0013] At least some of these objects are achieved by the present invention as defined in the independent claims. The dependent claims relate to advantageous embodiments of the invention.

[0014] In a first aspect of the present invention, there is provided a method of signing video data, the method comprising obtaining video data representing a video sequence, obtaining a bit string not extracted from the video data, generating a salt by hashing the bit string, generating a first fingerprint, and providing a signature of the video data including the first fingerprint, wherein the first fingerprint is generated by hashing a combination of the salt and a first portion of the video data, or by hashing a combination of the salt and a hash of the first portion of the video data.

[0015] A recipient of the signed video data can use the signature to validate the authenticity or integrity of the video data, as well as ensure non-repudiation. Even if an unauthorized party knows a first portion of the video data and a first fingerprint generated from it, it becomes very difficult for them to guess which hash function was used, because the first portion of the video data (or its hash) is modified by the salt each time. This also prevents anyone without the bit string from generating a new fingerprint, e.g., one that references inauthentic video data. Third, because the bit string is not extracted from the video data, the probability that an identical bit string will appear in the video data is very small, and therefore, for all practical purposes, the bit string can be considered independent of the video data. Using a non-content-based salt allows a recipient to complete the verification process without receiving the entire video data, as in video streaming applications.

[0016] In this disclosure, a "hash" of a data item B1 includes both the primary hash h(B1) and higher-order hashes obtained by recursive hashing. This term covers at least the following examples: h(h(B1))=(h○h)(B1) (h○...○h)(B1) h({h(B1),h(B2)}) where B2 is a further data item and {·} represents a data combination operation such as concatenation. Thus, a "hash of a first portion of video data" includes the primary hash of said portion, as well as a hash of this hash, or a hash of a combination of each hash.

[0017] In some embodiments, the first portion of the video data is the entire video data. In other embodiments, the first portion of the video data, together with the second, third, and further portions from which fingerprints are taken, make up the entire video data. In yet other embodiments, fingerprinting is applied to only a subset of the video data. Here, for example, the video data may be partitioned into segments, and each fingerprint may be generated from a subset of the segments. In such embodiments, the subset is extracted in a pre-agreed manner that allows the extraction to be repeated by a recipient wishing to verify the signature. In such embodiments, for example, the first portion may be a subset of a data structure encoding a first video frame, and the second portion may be a subset of a data structure encoding a second video frame, with both subsets extracted using the same pre-agreed extraction algorithm. In relation to the aforementioned goal of protecting the secret function from being guessed, it can be understood that the secret function includes both a hash function and a subset extraction algorithm. Even if the subset extraction is repeated in the same manner for the first, second, and further portions of the video data, each resulting fingerprint will be modified by the salt such that an attacker faces a computationally very complex inversion problem. Preferably, the subsets account for a significant proportion of the video data or are sufficiently distributed throughout the video data to provide a high degree of confidence that the received video data has not been manipulated by an unauthorized party.

[0018] As mentioned above, the method may further include generating a second fingerprint based on the second portion of the video data and the salt previously generated from the bit string. Like the first fingerprint, the second fingerprint may be generated by hashing a combination of the salt and the second portion of the video data, or by hashing a combination of the salt and a hash of the second portion of the video data. Advantageously, even if the same salt is used for both fingerprints, the hash function used to generate the fingerprints remains secure against easy guessing. The salt may be conveniently cached in memory during the time that elapses between the generation of the first fingerprint and the generation of the second fingerprint. In connection with this embodiment, the first and second portions of the video data may represent (e.g., may be encoded as) respective time segments of a video sequence. The time segments may constitute frames of the video sequence. Alternatively, the time segments may constitute respective groups of pictures (GOPs) of the video sequence, where a GOP is defined as an independently decodable segment. To the extent that a GOP contains unidirectionally (forward) predicted or bidirectionally predicted frames, they can be decoded without relying on frames outside the GOP. Time segments may be disjoint, overlapping, or partially overlapping. For the avoidance of doubt, a preferred option is to use data encoding each video frame or each GOP, rather than plaintext video frames or plaintext GOPs, as the first portion, second portion, etc. of video data.

[0019] In one embodiment, the salt is generated using a first hash function, and the first (second, third, etc.) fingerprint is generated using a second, different hash function. The first hash function is kept secret. To achieve this, the method includes sharing the definition of the first hash function with a recipient of the signed video data over a dedicated communication channel. This allows the recipient to verify the signature of the video data by repeating this operation. Even if the definition of the hash function is shared over a dedicated communication channel, this embodiment allows the signature and / or video data to be transmitted over any communication channel without significantly compromising the security of the signing device. A dedicated communication channel may refer to a digital transmission path where unauthorized eavesdropping is extremely difficult and / or easily detectable. Encrypted communications and communications requiring two-channel authorization are examples of this type of dedicated communication channel. Furthermore, the definition of the hash function may be shared in an embedded manner by granting the recipient access to software configured in light of the hash function used, which may be, for example, a video decryption application or a signature verification application. In this way, the definition of the hash function is provided to the receiver's service without being verifiable in the clear. Yet another option is to place this definition of the hash function in a secure memory space of some device to which the device owner exclusively controls access. This device may, for example, be a digital video camera used to record video data. The secure memory space may also be physically located on a removable medium such as a chip or chipset (e.g., a Trusted Platform Module (TPM) or Secure Element (SE)), with the sender and receiver each holding one copy. A higher level of trust can be achieved if the definition of the hash function is split into two parts held by different users at the receiver's end, who are then asked to collaboratively verify the signature.

[0020] In one embodiment, the original bit string from which the salt is generated contains reproducible information related to the capture of the video sequence. This information is intended to be reproducible in the sense that the intended recipient can obtain the bit string without assistance from the signer who provided the signature of the video data. Alternatively, according to a further embodiment, at least a portion of the bit string is extracted from metadata associated with the video data. In yet another embodiment, the signature of the video contains the bit string in plaintext. This does not necessarily represent a vulnerability, particularly if the hash function from which the salt is generated (the first hash function) is kept secret between the signer and the recipient.

[0021] In another embodiment, the bit string from which the salt is generated is selected by the sender, who then inserts information from which the bit string is derivable into metadata associated with the video data. For example, the bit string may be derived from a prime factorization TIFF0007720821000001.tif8170 where M is an integer and salt is the prime factors p1, p2, ..., p t It is a hash of the combination of

[0022] In some embodiments, a signature of video data consists of multiple subsignatures, each associated with a respective (e.g., consecutive) segment of the video data. This is particularly useful when the video data has a time-series structure. The step of providing a signature may then include inserting said subsignatures into each segment of the video data. More specifically, the subsignatures may be inserted into the video bitstream in the vicinity of (i.e., at or near) each time segment, or the subsignatures may be included in metadata associated with such time segments. Insertion of a subsignature may be considered to be achieved "at or near" a time segment if verification of the subsignature does not appreciably delay or interfere with a decryption operation performed in parallel with this verification operation, for example, in a video playback application at the recipient's end.

[0023] In a second aspect of the present invention, there is provided an apparatus configured to carry out the above method. Broadly speaking, the second aspect of the present invention shares the effects and advantages of the first aspect and can be implemented with a corresponding degree of technical variation.

[0024] The present invention further relates to a computer program comprising instructions for enabling a computer to carry out the above-described method. This computer program may be stored on or distributed on a data carrier. In this specification, a "data carrier" may be a transitory data carrier, such as a modulated electromagnetic or light wave, or a non-transitory data carrier. Non-transitory data carriers include volatile and non-volatile memories, such as permanent and non-permanent storage media of the magnetic, optical, or solid-state type. Also within the scope of "data carrier," such memories may be fixedly attached or portable.

[0025] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art unless expressly stated otherwise herein. Any reference to "a / an / the (element, device, component, means, step, etc.)" should be interpreted straightforwardly as referring to at least one instance of such element, device, component, means, step, etc. unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order described unless explicitly stated otherwise.

[0026] Aspects and embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a flow diagram of a method for signing video data according to one embodiment of the present invention. [Figure 2] 1 illustrates an apparatus configured to perform signing of video data according to one embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0028] Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. However, these aspects may be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of all aspects of the invention to those skilled in the art. Like numbers refer to like elements throughout this description.

[0029] Referring to FIG. 1, a method 100 for signing video data representing (e.g., encoding) a video sequence is described. The method 100 is performed by or on behalf of a signer to provide a signature that can be verified by a recipient. When appropriately configured, the method 100 may be implemented by a general-purpose programmable computer, i.e., a computer with associated input and output interfaces. Specifically, the method 100 may be performed by an apparatus 200, shown in block diagram form in FIG. 2. The apparatus 200 comprises a processing circuit 210, a memory 220, and an input / output interface 230 suitable for bidirectional communication with an external memory 290 that stores the video data to be signed during some operational phases. The apparatus 200 and the external memory 290 may be owned and operated by different entities, such as when signatures are provided as an external service, or by a common entity. The (internal) memory 220 of the device 200 may be suitable for storing a program 221 having software instructions for executing the method 100, cryptographic information (e.g., private keys) for generating signatures, variables, and cached data used in fingerprinting, as well as logs, configuration files, and data supporting various internal housekeeping procedures. The device 200 may be provided as a local computer or server, or may be implemented in a distributed manner based on networked (cloud) processing resources. In particular, the device 200 may be integrated into a digital video camera, such as a video camera suitable for surveillance applications, so that the method 100 can be performed on video data generated by this video camera before the video data is provided to an external recipient.

[0030] In a first step 110 of method 100, video data representing a video sequence is obtained. This video data may, but need not, have a definite scope (duration). Rather, recording of the video sequence may still be ongoing, as is often the case in streaming applications, including live streaming and video surveillance applications. Known decoding processes exist that are adapted to handle video data that is incomplete in the sense that it can be supplemented by relatively recent data; one notable example is the technique described in Recommendation ITU-T H.264 (06 / 2019) “Advanced video coding for generic audiovisual services” (International Telecommunication Union). Similarly, method 100 was devised out of a desire to allow signature verification to proceed in parallel with this type of decoding process without delay or interference. The act of obtaining the video data may include gaining access to a memory (e.g., external memory 290 in FIG. 2 ) in which the video data is stored, downloading the video data, and / or receiving a transmission involving the video data.

[0031] In a second step 112, a bit string b is obtained that has not been extracted from the video data. This bit string b is a series of binary values. This method 100 does not assume that the bit string indicates, represents, or encodes any information. However, to facilitate the recipient's reproduction of the bit string, the bit string may include the time, date, or position of the capture (recording) of the video sequence. This capture time may refer to the beginning or end. For live or streaming video sequences, it is conceivable to repeatedly generate a new salt based on a new bit string. For example, if the bit string refers to the beginning of a consecutive segment of a recording, the signature will be ready for verification as soon as capture begins, and a high level of security can be maintained by having the new salt replace the previous salt. Another option is to extract the bit string from metadata associated with the video data, such as file system parameters or file format metadata. Yet another option is to insert original information into such metadata from which the bit string can be derived by a pre-agreed operation.

[0032] Based on the bit string b, in a third step 114, a salt is generated by hashing the bit string, i.e., σ = h1(b). This hashing is performed by a hash function (or one-way function) h1. This may be a cryptographic hash function that provides a level of security deemed appropriate given the sensitivity of the video data being signed. Three examples are SHA-256, SHA3-512, and RSA-1024. The hash function h1 shall be predefined (e.g., reproducible) so that the salt, and thereby the fingerprint, can be regenerated when the fingerprint is verified. In some embodiments, this hash function h1 is kept secret between the signer and the recipient, which may require the definition of the hash function to be securely shared with the recipient (120). Such step 120, which will be described below, may be performed at any suitable time before, during, or after further steps of method 100, independent of such steps.

[0033] One realization of the above option is now described, in which original information from which a bit string can be derived by a pre-agreed operation is inserted into the metadata. In this realization, said information is an integer M chosen by the sender. This choice may be random. This integer is: Prime factors p1, p2, ... p as in TIFF0007720821000002.tif9170 t where q1,...q t ≥ 1. The salt is computed as a hash of the prime factors combined in ascending, descending, or another pre-agreed order, e.g., σ = h1({p1, p2, ..., p t}) or σ=h1({p t ,p t-1,...,p1}). This allows the receiver to take the integer M from the metadata, perform the prime factorization, recalculate the salt, and verify the signature of the video data. It is recalled that prime factorization produces a unique result. Therefore, this may be a pre-agreed operation in this sense, if used together with an ordering of the resulting factors, such as ascending or descending.

[0034] In a fourth step 116 of method 100, fingerprints F1, F2, ... are generated by hashing the video content. For purposes of illustration, it will first be assumed that fingerprinting is performed at the granularity of one video frame. Both finer and coarser granularities are valid alternatives to this, including fingerprinting predefined image bands (macroblocks) of consecutive frames, or fingerprinting consecutive groups of pictures (GOPs).

[0035] Meanwhile, the fourth step 116 may include hashing the combination of the salt σ and the first portion π1 of the video data. F1=h2({σ,π1}) where h2 is the second hash function. The first and second hash functions may be the same, h1 = h2, or they may be different. The curly bracket notation {·} refers to a general-purpose data combination operation, which may include concatenating data linearly (juxtaposition) or in various staggered arrangements. The combination operation may further include arithmetic operations on the data, such as bitwise OR, XOR, multiplication, division, or modulo operations. Further fingerprints F2, F3, ... can be calculated analogously, i.e., F n =h2({σ,π n}) and n≧2. In particular, a preferred option is not to replace the salt σ: rather, the salt can be cached after computing the first fingerprint F1 (114.1) and retrieved for later use when the second and further fingerprints are generated.

[0036] Meanwhile, the fourth step 116 may involve hashing a combination of the salt σ and the hash of the first portion π1 of the video data. A simple implementation is as follows: F1=({σ,h2(π1)}) A further possible implementation is to use higher order hashes. F1=h2({σ,h2(h2(π1))})

[0037] According to two further implementations, which may be particularly suitable for use cases where the available bitrate is limited, one fingerprint is generated per GOP. The first implementation generates a fingerprint for every frame π1, π2, ..., π N The goal is to generate a fingerprint for the GOP based on a hash of a combination of the hashes of the GOPs. F GOP1 =h2({σ,h2({h2(π1),h2(π2),...,h2(π N )})}) The second implementation is to generate fingerprints of the GOPs iteratively. TIFF0007720821000003.tif45170 where, TIFF0007720821000004.tif8170 is a temporary variable that may be discarded once the next element in the sequence has been successfully calculated. In the second implementation, as in the first implementation, h2(π1), h2(π2), ..., h2(π N ) is eliminated. Hash linking also protects against unauthorized removal, insertion, and reordering of frames within a GOP.

[0038] In a variation of the above option, the hash function used to perform the internal hashing operation(s) can be replaced by a third hash function h3 that is different from the second hash function h2 used for the external operation.

[0039] A common advantage of this second group of implementations of the fourth step 116 stems from the fact that the length of the hash is fixed and, moreover, typically much shorter than the data required to encode one video frame or one GOP. Thus, the combination of salting and hashing the video data can be achieved with lightweight memory operations that have limited computational cost.

[0040] In a fifth step 118, a signature of the video data is provided, which includes at least one of the generated fingerprints F1, F2, .... This signature may be formed by collecting the generated fingerprints in a so-called document (a text file or another data structure) and signing this document. For example, the document signature may be generated by asymmetric cryptography, i.e., using a private key from a key pair whose public key is previously shared with the recipient so that the recipient can verify the signature. Thus, the signature of the video sequence may consist of the document and the document signature. Optionally, if the first hash function h1 is kept secret, a bit string b may be included in the signature.

[0041] Another option is to provide (118) a signature consisting of several sub-signatures S1, S2, S3, .... The sub-signatures may relate to consecutive segments of video data, in particular time segments. If GOP-level signatures are applied, the fifth step 118 may also include providing, for each GOP, a document carrying the signatures of each frame within this GOP, and generating a signature for the document. Alternatively, according to the low bitrate option mentioned above, the document may be F GOP1In any case, the step 118 of providing a signature may include inserting said subsignatures S1, S2, S3, ... into respective segments of the video data. More specifically, the subsignatures may be inserted into the video bitstream near each time segment, or the subsignatures may be included in the metadata associated with such time segments. In particular, a GOP-level subsignature may be included in the metadata of the first or last frame of a GOP, or by inserting a subsignature into the video bitstream near such frames. This may support the so-called intra-update option in the ITU-T H.264 format.

[0042] Optionally, method 100 may include an additional step 120 in which the definition of the first hash function h1 that generates the salt σ is shared with the recipient of the signed video data via a dedicated communication channel. As previously described, a dedicated communication channel may refer to a digital transmission path protected from unauthorized eavesdropping, including encrypted communication and communication requiring two-channel authorization. The hash function definition may also be shared in various embedded formats via decryption software or hardware. It is understood that the definition of the first hash function h1 may be incomplete or limited to specific configuration parameters, and that this first hash function h1 shall have a standardized or otherwise pre-agreed format. Step 120 may be performed before, after, or in parallel with other steps of method 100.

[0043] Aspects of the present disclosure have been described above primarily with reference to certain embodiments. However, as will be readily apparent to those skilled in the art, other embodiments beyond those disclosed above are equally feasible within the scope of the present invention as defined by the appended claims. In fact, method 100 is not limited to encoded video data and may be performed on unencoded (i.e., plaintext) video data. Method 100 is also applicable to additional encoded video formats, such as AOMedia Video1 (AV1) and formats specified in Recommendation ITU-T H.265 (08 / 2021) "High efficiency video coding." [Explanation of symbols]

[0044] 100 ways 110 First Step 112 Second Step 114 Third Step 116 Fourth Step 118 The Fifth Step 120 additional steps 200 equipment 210 Processing circuit 220 memory 221 Program 230 Input / Output Interface 290 external memory

Claims

1. A method (100) for signing video data, comprising: obtaining (110) video data representing a video sequence; obtaining (112) an unextracted bit string from the video data; providing a salt based on the bit string; a) a combination of the salt and a first portion of the video data; or b) combining the salt with a hash of a first portion of the video data; generating a first fingerprint by hashing (116.1); providing a signature of the video data, the signature including the first fingerprint (118); Including, The salt is provided by hashing (114) the bit string, and the salt and the first fingerprint are generated using different hash functions, and the method further comprises: Sharing (220) the definition of the hash function for generating the salt with a recipient of the signed video data via a dedicated communication channel. A method comprising:

2. a) a combination of the salt and a second portion of the video data; or b) combining the salt with a hash of a second portion of the video data; generating a second fingerprint by hashing (116.2) The method of claim 1 , wherein the signature of the video data further includes the second fingerprint.

3. The method of claim 2 , wherein the first portion and the second portion represent respective time segments of the video sequence.

4. The method of claim 3 , wherein the first portion and the second portion represent respective frames of the video sequence.

5. The method of claim 3 , wherein the first portion and the second portion represent respective independently decodable groups of pictures (GOPs) of the video sequence.

6. Caching the salt (114.1) 3. The method of claim 2, further comprising: generating the second fingerprint (116.2) using the cached salt.

7. The method of claim 1 , wherein the first portion of the video data is any of the captured video data.

8. the bit string contains reproducible information related to the capture of the video sequence; at least a portion of the bit string is extracted from metadata associated with the video data; information from which the bit string can be uniquely derived is inserted into metadata associated with the video data; the signature of the video data further includes the bit string; The method of claim 1 , wherein at least one of the following holds true:

9. The method of claim 1 , wherein the video sequence is a streaming video sequence.

10. the video data has a time-series structure, and the signature is comprised of a plurality of sub-signatures associated with respective segments of the video data; 10. The method of claim 9, wherein the signature is provided by inserting the sub-signature in or near the respective segment of the video data (118).

11. The method of claim 1 , wherein the signature of the video data is included in metadata associated with the video data.

12. The method of claim 1 , wherein the signature of the video data is cryptographically signed.

13. An apparatus (200) comprising a processing circuit (210) configured to perform the method of any one of claims 1 to 12.

14. A computer program (221) comprising instructions that, when executed by a computer, cause the computer to perform a method according to any one of claims 1 to 12.

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