C2PASigner Class

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Creates a C2PA Manifest, signs it, and embeds it into an asset.

Syntax

class ipworksllm.C2PASigner

Remarks

The C2PASigner class produces Content Credentials: a signed C2PA Manifest that records how an asset was produced, which tool produced it, and whether generative AI was involved. The manifest is embedded directly into the asset, so the provenance travels with the file.

Supported Formats

The class embeds the manifest into the asset itself, so each container format needs its own support. JPEG, PNG and PDF are supported.

The format is detected from the asset itself; there is nothing to configure. An asset in any other format is refused rather than written incorrectly.

For PDF, only documents using classic cross-reference tables can be signed. A document using cross-reference streams is refused, because appending a table-style update to it would produce a file that readers reject.

Signing an Asset

Set input_file to the asset to be signed, output_file to the destination, and signing_cert to a certificate with an associated private key. Calling sign builds the manifest, signs it, and writes the result.

C2PASigner signer = new C2PASigner(); signer.InputFile = "photo.jpg"; signer.OutputFile = "photo-signed.jpg"; signer.ClaimGenerator = "MyApp/1.0"; signer.SigningCert = new Certificate(CertStoreTypes.cstPFXFile, "signer.pfx", "password", "*"); signer.Sign();

The signing certificate must carry the C2PA claim signing extended key usage, and the manifest is signed with the algorithm named by signature_algorithm. The permitted algorithms are ES256, ES384, ES512, PS256, PS384, PS512, and Ed25519; the C2PA specification permits no others.

Disclosing AI-Generated Content

The most common reason to sign an asset is to disclose how it was created. The add_action method records a single action in the manifest. Marking an asset as generative AI output is one call.

signer.AddAction("c2pa.created", "http://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia", "MyApp/1.0"); signer.Sign();

The second parameter is the digital source type. The C2PA specification requires that a digital source type accompany the c2pa.created action for every asset; use http://c2pa.org/digitalsourcetype/empty when the asset began as a new file with no digital content.

Adding Other Assertions

Anything beyond the assertions the class computes for itself is added with add_assertion, which appends a raw assertion payload under a given label. This keeps the API stable as the C2PA standard assertion set evolves.

string creativeWork = "{\"@context\":\"https://schema.org\",\"@type\":\"CreativeWork\",\"author\":[{\"@type\":\"Person\",\"name\":\"Jane Doe\"}]}"; signer.AddAssertion("stds.schema-org.CreativeWork", "application/json", System.Text.Encoding.UTF8.GetBytes(creativeWork));

The content binding assertion, which cryptographically ties the manifest to the asset bytes, is always computed by the class and cannot be supplied by the application. Doing so is what makes tampering detectable.

Trusted Time-Stamps

Setting tsaurl to the address of an RFC 3161 Time Stamping Authority adds a trusted time-stamp to the signature. A time-stamped signature remains verifiable after the signing certificate expires, which is why the C2PA specification recommends obtaining one whenever a TSA can be reached.

signer.TSAURL = "http://timestamp.example.com/tsa"; signer.Sign();

Property List

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The following is the full list of the properties of the class with short descriptions. Click on the links for further details.

Method List

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The following is the full list of the methods of the class with short descriptions. Click on the links for further details.

Event List

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The following is the full list of the events fired by the class with short descriptions. Click on the links for further details.

Config Settings

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The following is a list of config settings for the class with short descriptions. Click on the links for further details.

action_count property

The number of records in the Action arrays.

Syntax

def get_action_count() -> int: ...

def set_action_count(value: int) -> None: ...


action_count = property(get_action_count, set_action_count)

Default Value

0

Remarks

This property controls the size of the following arrays:

• action
• action_digital_source_type
• action_software_agent
• action_when

The array indices start at 0 and end at action_count - 1.

action property

The action identifier.

Syntax

def get_action(action_index: int) -> str: ...

def set_action(action_index: int, value: str) -> None: ...

Default Value

""

Remarks

The action identifier.

This field holds the C2PA action identifier. Values defined by the specification include c2pa.created, c2pa.edited, c2pa.opened, c2pa.placed, c2pa.converted, and c2pa.published.

The first action in a manifest describes how the asset came into being, and is normally c2pa.created.

The action_index parameter specifies the index of the item in the array. The size of the array is controlled by the action_count property.

action_digital_source_type property

The nature of the content the action produced.

Syntax

def get_action_digital_source_type(action_index: int) -> str: ...

def set_action_digital_source_type(action_index: int, value: str) -> None: ...

Default Value

""

Remarks

The nature of the content the action produced.

This field identifies what kind of content resulted from the action, using a term from the IPTC digital source type vocabulary or one of the C2PA-specific values.

The C2PA specification requires that a digital source type accompany the c2pa.created action for every asset. Commonly used values are:

No digital source type is required with a c2pa.opened action.

The action_index parameter specifies the index of the item in the array. The size of the array is controlled by the action_count property.

action_software_agent property

The tool that performed the action.

Syntax

def get_action_software_agent(action_index: int) -> str: ...

def set_action_software_agent(action_index: int, value: str) -> None: ...

Default Value

""

Remarks

The tool that performed the action.

This field names the software that carried out the action, for example MyApp/1.0.

It answers a different question from the manifest's claim generator: the claim generator is whatever wrote the provenance data, while this field is whatever actually edited the asset. They are often, but not always, the same tool.

The action_index parameter specifies the index of the item in the array. The size of the array is controlled by the action_count property.

action_when property

When the action took place.

Syntax

def get_action_when(action_index: int) -> str: ...

def set_action_when(action_index: int, value: str) -> None: ...

Default Value

""

Remarks

When the action took place.

This field holds the time the action was performed, as an RFC 3339 date and time.

The C2PA specification requires an explicit timezone or a trailing Z for UTC. When this field is left empty, no time is recorded for the action.

Note that this is a claimed time, asserted by whoever signed the manifest. It is not the same as a trusted time-stamp, which is obtained from a Time Stamping Authority and is what a validator relies on to establish when the signature actually existed.

The action_index parameter specifies the index of the item in the array. The size of the array is controlled by the action_count property.

assertion_count property

The number of records in the Assertion arrays.

Syntax

def get_assertion_count() -> int: ...

def set_assertion_count(value: int) -> None: ...


assertion_count = property(get_assertion_count, set_assertion_count)

Default Value

0

Remarks

This property controls the size of the following arrays:

• assertion_data
• assertion_label
• assertion_media_type

The array indices start at 0 and end at assertion_count - 1.

assertion_label property

The assertion label.

Syntax

def get_assertion_label(assertion_index: int) -> str: ...

def set_assertion_label(assertion_index: int, value: str) -> None: ...

Default Value

""

Remarks

The assertion label.

This field holds the C2PA assertion label, which identifies what kind of statement the assertion makes and therefore how assertion_data should be interpreted.

Examples are c2pa.actions.v2, c2pa.hash.data, stds.schema-org.CreativeWork, and stds.exif.

The assertion_index parameter specifies the index of the item in the array. The size of the array is controlled by the assertion_count property.

assertion_data property

The assertion payload.

Syntax

def get_assertion_data(assertion_index: int) -> bytes: ...

def set_assertion_data(assertion_index: int, value: bytes) -> None: ...

Default Value

""

Remarks

The assertion payload.

This field holds the assertion's payload, encoded according to assertion_media_type.

The payload is passed through verbatim in both directions. An application can therefore write assertion types the class has no built-in knowledge of, and read back ones added to the standard after the class was built.

The assertion_index parameter specifies the index of the item in the array. The size of the array is controlled by the assertion_count property.

assertion_media_type property

The media type of the assertion payload.

Syntax

def get_assertion_media_type(assertion_index: int) -> str: ...

def set_assertion_media_type(assertion_index: int, value: str) -> None: ...

Default Value

"application/cbor"

Remarks

The media type of the assertion payload.

This field holds the media type of assertion_data, normally application/cbor or application/json.

The C2PA specification requires that assertions it defines be serialized as CBOR, so application/cbor is the default.

The assertion_index parameter specifies the index of the item in the array. The size of the array is controlled by the assertion_count property.

claim_generator property

The identifier of the tool that created the claim.

Syntax

def get_claim_generator() -> str: ...

def set_claim_generator(value: str) -> None: ...


claim_generator = property(get_claim_generator, set_claim_generator)

Default Value

""

Remarks

This property identifies the application that produced the C2PA Manifest, and is recorded in the claim so a consumer can see which tool made the provenance assertion.

Use a name and version, for example MyApp/1.0. When this property is left empty, the class records its own name and version.

ingredient_count property

The number of records in the Ingredient arrays.

Syntax

def get_ingredient_count() -> int: ...

def set_ingredient_count(value: int) -> None: ...


ingredient_count = property(get_ingredient_count, set_ingredient_count)

Default Value

0

Remarks

This property controls the size of the following arrays:

• ingredient_format
• ingredient_instance_id
• ingredient_manifest_label
• ingredient_relationship
• ingredient_title

The array indices start at 0 and end at ingredient_count - 1.

ingredient_format property

The media type of the ingredient asset.

Syntax

def get_ingredient_format(ingredient_index: int) -> str: ...

def set_ingredient_format(ingredient_index: int, value: str) -> None: ...

Default Value

""

Remarks

The media type of the ingredient asset.

This field holds the media type of the asset that went into this one, for example image/jpeg, image/png or application/pdf. The class fills it in from the source asset when the ingredient is added.

The ingredient_index parameter specifies the index of the item in the array. The size of the array is controlled by the ingredient_count property.

ingredient_instance_id property

The instance identifier of the ingredient asset.

Syntax

def get_ingredient_instance_id(ingredient_index: int) -> str: ...

def set_ingredient_instance_id(ingredient_index: int, value: str) -> None: ...

Default Value

""

Remarks

The instance identifier of the ingredient asset.

This field holds the identifier of the exact version of the asset that went into this one, normally an XMP instance identifier such as xmp:iid:....

When the ingredient carried a C2PA Manifest of its own, the class fills this in from that Manifest's claim, so the reference names the precise version that was used rather than the document in general.

Version 2 of the ingredient assertion also carried a document identifier. Version 3, which this class writes, removed it, so there is no corresponding field.

The ingredient_index parameter specifies the index of the item in the array. The size of the array is controlled by the ingredient_count property.

ingredient_manifest_label property

The label of the ingredient's own C2PA Manifest.

Syntax

def get_ingredient_manifest_label(ingredient_index: int) -> str: ...

def set_ingredient_manifest_label(ingredient_index: int, value: str) -> None: ...

Default Value

""

Remarks

The label of the ingredient's own C2PA Manifest.

This field identifies the manifest that describes the ingredient, when the ingredient carried one. It is the urn:c2pa label of that manifest within the same manifest store.

An empty value means the ingredient arrived without provenance data of its own.

The ingredient_index parameter specifies the index of the item in the array. The size of the array is controlled by the ingredient_count property.

ingredient_relationship property

How the ingredient relates to the asset.

Syntax

def get_ingredient_relationship(ingredient_index: int) -> str: ...

def set_ingredient_relationship(ingredient_index: int, value: str) -> None: ...

Default Value

"componentOf"

Remarks

How the ingredient relates to the asset.

This field describes the ingredient's role. The C2PA specification defines the following values:

The default value is componentOf.

The ingredient_index parameter specifies the index of the item in the array. The size of the array is controlled by the ingredient_count property.

ingredient_title property

A human-readable name for the ingredient.

Syntax

def get_ingredient_title(ingredient_index: int) -> str: ...

def set_ingredient_title(ingredient_index: int, value: str) -> None: ...

Default Value

""

Remarks

A human-readable name for the ingredient.

This field holds a title for the ingredient asset, typically its filename, so a consumer can present the provenance chain in terms a person recognises.

The ingredient_index parameter specifies the index of the item in the array. The size of the array is controlled by the ingredient_count property.

input_data property

The asset to process, held in memory.

Syntax

def get_input_data() -> bytes: ...

def set_input_data(value: bytes) -> None: ...


input_data = property(get_input_data, set_input_data)

Default Value

""

Remarks

This property specifies the asset to be processed as a byte array, for applications that do not work with files on disk.

When both input_file and this property are set, input_file takes precedence.

input_file property

The asset to process.

Syntax

def get_input_file() -> str: ...

def set_input_file(value: str) -> None: ...


input_file = property(get_input_file, set_input_file)

Default Value

""

Remarks

This property specifies the asset to be processed. Set it to the full or relative path of the file.

When both this property and input_data are set, this property takes precedence.

output_data property

The signed asset, held in memory.

Syntax

def get_output_data() -> bytes: ...


output_data = property(get_output_data, None)

Default Value

""

Remarks

This property holds the signed asset after the operation completes, when output_file was left empty.

This property is read-only.

output_file property

The file to write the signed asset to.

Syntax

def get_output_file() -> str: ...

def set_output_file(value: str) -> None: ...


output_file = property(get_output_file, set_output_file)

Default Value

""

Remarks

This property specifies where the signed asset is written. Set it to the full or relative path of the destination file.

If this property is empty, the signed asset is written to output_data instead.

An error is thrown if the file already exists and overwrite is False.

overwrite property

Whether the class may overwrite an existing output file.

Syntax

def get_overwrite() -> bool: ...

def set_overwrite(value: bool) -> None: ...


overwrite = property(get_overwrite, set_overwrite)

Default Value

False

Remarks

This property indicates whether the class will overwrite output_file. When it is False, an error is thrown if output_file already exists.

The default value is False.

signature_algorithm property

The algorithm used to sign the claim.

Syntax

def get_signature_algorithm() -> str: ...

def set_signature_algorithm(value: str) -> None: ...


signature_algorithm = property(get_signature_algorithm, set_signature_algorithm)

Default Value

"ES256"

Remarks

This property specifies the signature algorithm. The C2PA specification permits only the following values, and no others:

The value must be compatible with the key in signing_cert. The default value is ES256.

signing_cert_effective_date property

The date on which this certificate becomes valid.

Syntax

def get_signing_cert_effective_date() -> str: ...


signing_cert_effective_date = property(get_signing_cert_effective_date, None)

Default Value

""

Remarks

The date on which this certificate becomes valid. Before this date, it is not valid. The date is localized to the system's time zone. The following example illustrates the format of an encoded date:

23-Jan-2000 15:00:00.

This property is read-only.

signing_cert_encoded property

The certificate (PEM/Base64 encoded).

Syntax

def get_signing_cert_encoded() -> bytes: ...

def set_signing_cert_encoded(value: bytes) -> None: ...


signing_cert_encoded = property(get_signing_cert_encoded, set_signing_cert_encoded)

Default Value

""

Remarks

The certificate (PEM/Base64 encoded). This property is used to assign a specific certificate. The signing_cert_store and signing_cert_subject properties also may be used to specify a certificate.

When signing_cert_encoded is set, a search is initiated in the current signing_cert_store for the private key of the certificate. If the key is found, signing_cert_subject is updated to reflect the full subject of the selected certificate; otherwise, signing_cert_subject is set to an empty string.

signing_cert_expiration_date property

The date on which the certificate expires.

Syntax

def get_signing_cert_expiration_date() -> str: ...


signing_cert_expiration_date = property(get_signing_cert_expiration_date, None)

Default Value

""

Remarks

The date on which the certificate expires. After this date, the certificate will no longer be valid. The date is localized to the system's time zone. The following example illustrates the format of an encoded date:

23-Jan-2001 15:00:00.

This property is read-only.

signing_cert_extended_key_usage property

A comma-delimited list of extended key usage identifiers.

Syntax

def get_signing_cert_extended_key_usage() -> str: ...


signing_cert_extended_key_usage = property(get_signing_cert_extended_key_usage, None)

Default Value

""

Remarks

A comma-delimited list of extended key usage identifiers. These are the same as ASN.1 object identifiers (OIDs).

This property is read-only.

signing_cert_fingerprint property

The hex-encoded, 16-byte MD5 fingerprint of the certificate.

Syntax

def get_signing_cert_fingerprint() -> str: ...


signing_cert_fingerprint = property(get_signing_cert_fingerprint, None)

Default Value

""

Remarks

The hex-encoded, 16-byte MD5 fingerprint of the certificate. This property is primarily used for keys which do not have a corresponding X.509 public certificate, such as PEM keys that only contain a private key. It is commonly used for SSH keys.

The following example illustrates the format: bc:2a:72:af:fe:58:17:43:7a:5f:ba:5a:7c:90:f7:02

This property is read-only.

signing_cert_fingerprint_sha1 property

The hex-encoded, 20-byte SHA-1 fingerprint of the certificate.

Syntax

def get_signing_cert_fingerprint_sha1() -> str: ...


signing_cert_fingerprint_sha1 = property(get_signing_cert_fingerprint_sha1, None)

Default Value

""

Remarks

The hex-encoded, 20-byte SHA-1 fingerprint of the certificate. This property is primarily used for keys which do not have a corresponding X.509 public certificate, such as PEM keys that only contain a private key. It is commonly used for SSH keys.

The following example illustrates the format: 30:7b:fa:38:65:83:ff:da:b4:4e:07:3f:17:b8:a4:ed:80:be:ff:84

This property is read-only.

signing_cert_fingerprint_sha256 property

The hex-encoded, 32-byte SHA-256 fingerprint of the certificate.

Syntax

def get_signing_cert_fingerprint_sha256() -> str: ...


signing_cert_fingerprint_sha256 = property(get_signing_cert_fingerprint_sha256, None)

Default Value

""

Remarks

The hex-encoded, 32-byte SHA-256 fingerprint of the certificate. This property is primarily used for keys which do not have a corresponding X.509 public certificate, such as PEM keys that only contain a private key. It is commonly used for SSH keys.

The following example illustrates the format: 6a:80:5c:33:a9:43:ea:b0:96:12:8a:64:96:30:ef:4a:8a:96:86:ce:f4:c7:be:10:24:8e:2b:60:9e:f3:59:53

This property is read-only.

signing_cert_issuer property

The issuer of the certificate.

Syntax

def get_signing_cert_issuer() -> str: ...


signing_cert_issuer = property(get_signing_cert_issuer, None)

Default Value

""

Remarks

The issuer of the certificate. This property contains a string representation of the name of the issuing authority for the certificate.

This property is read-only.

signing_cert_private_key property

The private key of the certificate (if available).

Syntax

def get_signing_cert_private_key() -> str: ...


signing_cert_private_key = property(get_signing_cert_private_key, None)

Default Value

""

Remarks

The private key of the certificate (if available). The key is provided as PEM/Base64-encoded data.

NOTE: The signing_cert_private_key may be available but not exportable. In this case, signing_cert_private_key returns an empty string.

This property is read-only.

signing_cert_private_key_available property

Whether a PrivateKey is available for the selected certificate.

Syntax

def get_signing_cert_private_key_available() -> bool: ...


signing_cert_private_key_available = property(get_signing_cert_private_key_available, None)

Default Value

False

Remarks

Whether a signing_cert_private_key is available for the selected certificate. If signing_cert_private_key_available is True, the certificate may be used for authentication purposes (e.g., server authentication).

This property is read-only.

signing_cert_private_key_container property

The name of the PrivateKey container for the certificate (if available).

Syntax

def get_signing_cert_private_key_container() -> str: ...


signing_cert_private_key_container = property(get_signing_cert_private_key_container, None)

Default Value

""

Remarks

The name of the signing_cert_private_key container for the certificate (if available). This functionality is available only on Windows platforms.

This property is read-only.

signing_cert_public_key property

The public key of the certificate.

Syntax

def get_signing_cert_public_key() -> str: ...


signing_cert_public_key = property(get_signing_cert_public_key, None)

Default Value

""

Remarks

The public key of the certificate. The key is provided as PEM/Base64-encoded data.

This property is read-only.

signing_cert_public_key_algorithm property

The textual description of the certificate's public key algorithm.

Syntax

def get_signing_cert_public_key_algorithm() -> str: ...


signing_cert_public_key_algorithm = property(get_signing_cert_public_key_algorithm, None)

Default Value

""

Remarks

The textual description of the certificate's public key algorithm. The property contains either the name of the algorithm (e.g., "RSA" or "RSA_DH") or an object identifier (OID) string representing the algorithm.

This property is read-only.

signing_cert_public_key_length property

The length of the certificate's public key (in bits).

Syntax

def get_signing_cert_public_key_length() -> int: ...


signing_cert_public_key_length = property(get_signing_cert_public_key_length, None)

Default Value

0

Remarks

The length of the certificate's public key (in bits). Common values are 512, 1024, and 2048.

This property is read-only.

signing_cert_serial_number property

The serial number of the certificate encoded as a string.

Syntax

def get_signing_cert_serial_number() -> str: ...


signing_cert_serial_number = property(get_signing_cert_serial_number, None)

Default Value

""

Remarks

The serial number of the certificate encoded as a string. The number is encoded as a series of hexadecimal digits, with each pair representing a byte of the serial number.

This property is read-only.

signing_cert_signature_algorithm property

The text description of the certificate's signature algorithm.

Syntax

def get_signing_cert_signature_algorithm() -> str: ...


signing_cert_signature_algorithm = property(get_signing_cert_signature_algorithm, None)

Default Value

""

Remarks

The text description of the certificate's signature algorithm. The property contains either the name of the algorithm (e.g., "RSA" or "RSA_MD5RSA") or an object identifier (OID) string representing the algorithm.

This property is read-only.

signing_cert_store property

The name of the certificate store for the client certificate.

Syntax

def get_signing_cert_store() -> bytes: ...

def set_signing_cert_store(value: bytes) -> None: ...


signing_cert_store = property(get_signing_cert_store, set_signing_cert_store)

Default Value

"MY"

Remarks

The name of the certificate store for the client certificate.

The signing_cert_store_type property denotes the type of the certificate store specified by signing_cert_store. If the store is password-protected, specify the password in signing_cert_store_password.

signing_cert_store is used in conjunction with the signing_cert_subject property to specify client certificates. If signing_cert_store has a value, and signing_cert_subject or signing_cert_encoded is set, a search for a certificate is initiated. Please see the signing_cert_subject property for details.

Designations of certificate stores are platform dependent.

The following designations are the most common User and Machine certificate stores in Windows:

When the certificate store type is cstPFXFile, this property must be set to the name of the file. When the type is cstPFXBlob, the property must be set to the binary contents of a PFX file (i.e., PKCS#12 certificate store).

signing_cert_store_password property

If the type of certificate store requires a password, this property is used to specify the password needed to open the certificate store.

Syntax

def get_signing_cert_store_password() -> str: ...

def set_signing_cert_store_password(value: str) -> None: ...


signing_cert_store_password = property(get_signing_cert_store_password, set_signing_cert_store_password)

Default Value

""

Remarks

If the type of certificate store requires a password, this property is used to specify the password needed to open the certificate store.

signing_cert_store_type property

The type of certificate store for this certificate.

Syntax

def get_signing_cert_store_type() -> int: ...

def set_signing_cert_store_type(value: int) -> None: ...


signing_cert_store_type = property(get_signing_cert_store_type, set_signing_cert_store_type)

Possible Values

0 # User
1 # Machine
2 # PFXFile
3 # PFXBlob
4 # JKSFile
5 # JKSBlob
6 # PEMKeyFile
7 # PEMKeyBlob
8 # PublicKeyFile
9 # PublicKeyBlob
10 # SSHPublicKeyBlob
11 # P7BFile
12 # P7BBlob
13 # SSHPublicKeyFile
14 # PPKFile
15 # PPKBlob
16 # XMLFile
17 # XMLBlob
18 # JWKFile
19 # JWKBlob
20 # SecurityKey
21 # BCFKSFile
22 # BCFKSBlob
23 # PKCS11
99 # Auto

Default Value

0

Remarks

The type of certificate store for this certificate.

The class supports both public and private keys in a variety of formats. When the cstAuto value is used, the class will automatically determine the type. This property can take one of the following values:

signing_cert_subject property

The subject of the certificate used for client authentication.

Syntax

def get_signing_cert_subject() -> str: ...

def set_signing_cert_subject(value: str) -> None: ...


signing_cert_subject = property(get_signing_cert_subject, set_signing_cert_subject)

Default Value

""

Remarks

The subject of the certificate used for client authentication.

This property must be set after all other certificate properties are set. When this property is set, a search is performed in the current certificate store to locate a certificate with a matching subject.

If a matching certificate is found, the property is set to the full subject of the matching certificate.

If an exact match is not found, the store is searched for subjects containing the value of the property.

If a match is still not found, the property is set to an empty string, and no certificate is selected.

The special value "*" picks a random certificate in the certificate store.

The certificate subject is a comma-separated list of distinguished name fields and values. For instance, "CN=www.server.com, OU=test, C=US, E=example@email.com". Common fields and their meanings are as follows:

If a field value contains a comma, it must be quoted.

signing_cert_subject_alt_names property

Comma-separated lists of alternative subject names for the certificate.

Syntax

def get_signing_cert_subject_alt_names() -> str: ...


signing_cert_subject_alt_names = property(get_signing_cert_subject_alt_names, None)

Default Value

""

Remarks

Comma-separated lists of alternative subject names for the certificate.

This property is read-only.

signing_cert_thumbprint_md5 property

The MD5 hash of the certificate.

Syntax

def get_signing_cert_thumbprint_md5() -> str: ...


signing_cert_thumbprint_md5 = property(get_signing_cert_thumbprint_md5, None)

Default Value

""

Remarks

The MD5 hash of the certificate. It is primarily used for X.509 certificates. If the hash does not already exist, it is automatically computed.

This property is read-only.

signing_cert_thumbprint_sha1 property

The SHA-1 hash of the certificate.

Syntax

def get_signing_cert_thumbprint_sha1() -> str: ...


signing_cert_thumbprint_sha1 = property(get_signing_cert_thumbprint_sha1, None)

Default Value

""

Remarks

The SHA-1 hash of the certificate. It is primarily used for X.509 certificates. If the hash does not already exist, it is automatically computed.

This property is read-only.

signing_cert_thumbprint_sha256 property

The SHA-256 hash of the certificate.

Syntax

def get_signing_cert_thumbprint_sha256() -> str: ...


signing_cert_thumbprint_sha256 = property(get_signing_cert_thumbprint_sha256, None)

Default Value

""

Remarks

The SHA-256 hash of the certificate. It is primarily used for X.509 certificates. If the hash does not already exist, it is automatically computed.

This property is read-only.

signing_cert_usage property

The text description of UsageFlags .

Syntax

def get_signing_cert_usage() -> str: ...


signing_cert_usage = property(get_signing_cert_usage, None)

Default Value

""

Remarks

The text description of signing_cert_usage_flags.

This value will be one or more of the following strings and will be separated by commas:

• Digital Signature
• Non-Repudiation
• Key Encipherment
• Data Encipherment
• Key Agreement
• Certificate Signing
• CRL Signing
• Encipher Only

If the provider is OpenSSL, the value is a comma-separated list of X.509 certificate extension names.

This property is read-only.

signing_cert_usage_flags property

The flags that show intended use for the certificate.

Syntax

def get_signing_cert_usage_flags() -> int: ...


signing_cert_usage_flags = property(get_signing_cert_usage_flags, None)

Default Value

0

Remarks

The flags that show intended use for the certificate. The value of signing_cert_usage_flags is a combination of the following flags:

Please see the signing_cert_usage property for a text representation of signing_cert_usage_flags.

This functionality currently is not available when the provider is OpenSSL.

This property is read-only.

signing_cert_version property

The certificate's version number.

Syntax

def get_signing_cert_version() -> str: ...


signing_cert_version = property(get_signing_cert_version, None)

Default Value

""

Remarks

The certificate's version number. The possible values are the strings "V1", "V2", and "V3".

This property is read-only.

tsaurl property

The address of an RFC 3161 Time Stamping Authority.

Syntax

def get_tsaurl() -> str: ...

def set_tsaurl(value: str) -> None: ...


tsaurl = property(get_tsaurl, set_tsaurl)

Default Value

""

Remarks

This property specifies the Time Stamping Authority contacted during signing. When it is set, the class obtains a trusted time-stamp over the signature and embeds it in the C2PA Manifest as a countersignature.

A time-stamped signature stays verifiable after the signing certificate expires, because a validator can establish that the signature existed while the certificate was still valid. The C2PA specification recommends obtaining a time-stamp whenever a TSA can be reached at signing time.

When this property is empty, no time-stamp is requested.

When it is set and the authority cannot be reached, or returns no token, signing fails rather than producing an untimestamped Manifest. Asking for a time-stamp and quietly getting none would leave a signature that looks complete but loses its meaning the day the certificate expires.

The connection to the authority is authenticated like any other: a TSA presenting an untrusted or expired certificate is refused. There is no event for overriding that decision.

add_action method

Records an action in the C2PA Manifest.

Syntax

def add_action(action: str, digital_source_type: str, software_agent: str) -> None: ...

Remarks

This method appends an action to the manifest's actions assertion, creating that assertion if it does not exist yet.

action is the C2PA action identifier, such as c2pa.created, c2pa.edited, c2pa.opened, or c2pa.placed.

digital_source_type describes the nature of the content the action produced. The C2PA specification requires that a digital source type accompany the c2pa.created action for every asset. Commonly used values are:

Other values defined by the IPTC digital source type vocabulary may also be used. Pass an empty string when the action does not take one; a c2pa.opened action, for example, requires none.

software_agent names the tool that performed the action.

Disclosing AI-generated content is a single call:

signer.AddAction("c2pa.created", "http://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia", "MyApp/1.0");

add_assertion method

Appends an assertion to the Assertions collection.

Syntax

def add_assertion(assertion_label: str, media_type: str, data: bytes) -> None: ...

Remarks

This method appends a new C2PAAssertion item to the assertions properties.

assertion_label is the C2PA assertion label, such as stds.schema-org.CreativeWork or stds.exif. media_type is the payload's media type, normally application/json or application/cbor. data is the assertion payload.

Passing the payload through verbatim keeps the API stable as the C2PA standard assertion set evolves: a new assertion type can be written without waiting for a new build of the class.

string creativeWork = "{\"@context\":\"https://schema.org\",\"@type\":\"CreativeWork\",\"author\":[{\"@type\":\"Person\",\"name\":\"Jane Doe\"}]}"; signer.AddAssertion("stds.schema-org.CreativeWork", "application/json", System.Text.Encoding.UTF8.GetBytes(creativeWork));

Use add_action instead when recording an action, since it builds the correctly structured actions assertion for you.

add_ingredient method

Records that an asset went into the one being signed.

Syntax

def add_ingredient(source_file: str, title: str, relationship: str) -> None: ...

Remarks

An ingredient is a source asset and the relationship it has to this one. Recording ingredients is what turns individual Manifests into a provenance chain: a consumer can follow an edited image back to the photograph it came from, and that one back to the camera that produced it.

SourceFile is the asset that went in. Title is a human-readable name for it; pass an empty string to omit it. Relationship is one of:

When the source carries a C2PA Manifest of its own, that Manifest is copied into the Manifest being written and the ingredient points at it. The chain then travels with the file: a verifier can follow it without needing the original source asset.

When the source carries no Manifest, the ingredient still records what the source was. The chain stops there, which is the truth about that asset rather than something to conceal.

Call this before Sign. Ingredients are read back through the Ingredients collection.

Example. Recording that an edited image came from a signed original:

C2PASigner signer = new C2PASigner(); signer.InputFile = "edited.jpg"; signer.OutputFile = "edited-signed.jpg"; signer.SigningCert = new Certificate(CertStoreTypes.cstPFXFile, "signer.pfx", "password", "*"); signer.ClaimGenerator = "Acme Editor/3.0"; // The photograph this edit was made from. Its Manifest travels along. signer.AddIngredient("original.jpg", "Original photograph", "parentOf"); signer.AddAction("c2pa.edited", "", "Acme Editor/3.0"); signer.Sign();

Example. Recording the sources of a generated image:

C2PASigner signer = new C2PASigner(); signer.InputFile = "generated.png"; signer.OutputFile = "generated-signed.png"; signer.SigningCert = cert; signer.ClaimGenerator = "Acme Generator/1.0"; signer.AddIngredient("reference.jpg", "Reference image", "inputTo"); // Disclose that the output is generative. signer.AddAction("c2pa.created", "http://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia", "Acme Generator/1.0"); signer.Sign();

config method

Sets or retrieves a configuration setting.

Syntax

def config(configuration_string: str) -> str: ...

Remarks

config is a generic method available in every class. It is used to set and retrieve configuration settings for the class.

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the class, access to these internal properties is provided through the config method.

To set a configuration setting named PROPERTY, you must call Config("PROPERTY=VALUE"), where VALUE is the value of the setting expressed as a string. For boolean values, use the strings "True", "False", "0", "1", "Yes", or "No" (case does not matter).

To read (query) the value of a configuration setting, you must call Config("PROPERTY"). The value will be returned as a string.

reset method

This method will reset the class.

Syntax

def reset() -> None: ...

Remarks

This method will reset the class's properties to their default values.

sign method

Builds, signs, and embeds a C2PA Manifest.

Syntax

def sign() -> None: ...

Remarks

This method reads the asset named by input_file (or held in input_data), builds a C2PA Manifest from the assertions properties, signs the claim with signing_cert, embeds the manifest into the asset, and writes the result to output_file (or output_data).

The following example signs a JPEG and discloses that it was produced by a generative model.

C2PASigner signer = new C2PASigner(); signer.InputFile = "photo.jpg"; signer.OutputFile = "photo-signed.jpg"; signer.ClaimGenerator = "MyApp/1.0"; signer.SigningCert = new Certificate(CertStoreTypes.cstPFXFile, "signer.pfx", "password", "*"); signer.AddAction("c2pa.created", "http://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia", "MyApp/1.0"); signer.Sign();

Signing is a two-pass operation. The manifest is embedded once at a reserved size so the final byte layout of the asset is known, the content binding hash is then computed over the asset outside the manifest's own bytes, and the real signature replaces the reservation. This is what allows the hash to cover an asset that contains the manifest.

An error is thrown when signing_cert has no private key, when signature_algorithm is incompatible with that key, or when the input asset is of a format the class cannot embed into.

on_error event

Fired when information is available about errors during data delivery.

Syntax

class C2PASignerErrorEventParams(object):
  @property
  def error_code() -> int: ...
  @property
  def description() -> str: ...
# In class C2PASigner:
@property
def on_error() -> Callable[[C2PASignerErrorEventParams], None]: ...
@on_error.setter
def on_error(event_hook: Callable[[C2PASignerErrorEventParams], None]) -> None: ...

Remarks

The on_error event is fired in case of exceptional conditions during message processing. Normally the class fails with an error.

The error_code parameter contains an error code, and the description parameter contains a textual description of the error. For a list of valid error codes and their descriptions, please refer to the Error Codes section.

on_log event

This event fires once for each log message.

Syntax

class C2PASignerLogEventParams(object):
  @property
  def log_level() -> int: ...
  @property
  def message() -> str: ...
  @property
  def log_type() -> str: ...
# In class C2PASigner:
@property
def on_log() -> Callable[[C2PASignerLogEventParams], None]: ...
@on_log.setter
def on_log(event_hook: Callable[[C2PASignerLogEventParams], None]) -> None: ...

Remarks

This event fires once for each log message generated by the class. The verbosity is controlled by the LogLevel setting.

log_level indicates the level of message. Possible values are as follows:

message is the log entry.

log_type identifies the type of log entry. Possible values are Info, Manifest, Signature, and Validation.

C2PASigner Config Settings

The class accepts one or more of the following configuration settings. Configuration settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the class, access to these internal properties is provided through the config method.

C2PASigner Config Settings

Base Config Settings

C2PASigner Errors

C2PASigner Errors