C2PASigner Component

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

Syntax

ipworksllm.C2PASigner

Remarks

The C2PASigner component 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 component 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 InputFile to the asset to be signed, OutputFile to the destination, and SigningCert 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 SignatureAlgorithm. 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 AddAction 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 component computes for itself is added with AddAssertion, 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 component 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 component 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 component 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 component 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 component with short descriptions. Click on the links for further details.

ActionCount Property (C2PASigner Component)

The number of records in the Action arrays.

Syntax

func (obj *C2PASigner) ActionCount() (int32, error)
func (obj *C2PASigner) SetActionCount(value int32) error

Default Value

0

Remarks

This property controls the size of the following arrays:

• Action
• ActionDigitalSourceType
• ActionSoftwareAgent
• ActionWhen

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

Data Type

int32

Action Property (C2PASigner Component)

The action identifier.

Syntax

func (obj *C2PASigner) Action(ActionIndex int32) (string, error)
func (obj *C2PASigner) SetAction(ActionIndex int32, value string) error

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 ActionIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ActionCount property.

Data Type

string

ActionDigitalSourceType Property (C2PASigner Component)

The nature of the content the action produced.

Syntax

func (obj *C2PASigner) ActionDigitalSourceType(ActionIndex int32) (string, error)
func (obj *C2PASigner) SetActionDigitalSourceType(ActionIndex int32, value string) error

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 ActionIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ActionCount property.

Data Type

string

ActionSoftwareAgent Property (C2PASigner Component)

The tool that performed the action.

Syntax

func (obj *C2PASigner) ActionSoftwareAgent(ActionIndex int32) (string, error)
func (obj *C2PASigner) SetActionSoftwareAgent(ActionIndex int32, value string) error

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 ActionIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ActionCount property.

Data Type

string

ActionWhen Property (C2PASigner Component)

When the action took place.

Syntax

func (obj *C2PASigner) ActionWhen(ActionIndex int32) (string, error)
func (obj *C2PASigner) SetActionWhen(ActionIndex int32, value string) error

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 ActionIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ActionCount property.

Data Type

string

AssertionCount Property (C2PASigner Component)

The number of records in the Assertion arrays.

Syntax

func (obj *C2PASigner) AssertionCount() (int32, error)
func (obj *C2PASigner) SetAssertionCount(value int32) error

Default Value

0

Remarks

This property controls the size of the following arrays:

• AssertionData
• AssertionLabel
• AssertionMediaType

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

Data Type

int32

AssertionLabel Property (C2PASigner Component)

The assertion label.

Syntax

func (obj *C2PASigner) AssertionLabel(AssertionIndex int32) (string, error)
func (obj *C2PASigner) SetAssertionLabel(AssertionIndex int32, value string) error

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 AssertionData should be interpreted.

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

The AssertionIndex parameter specifies the index of the item in the array. The size of the array is controlled by the AssertionCount property.

Data Type

string

AssertionData Property (C2PASigner Component)

The assertion payload.

Syntax

func (obj *C2PASigner) AssertionData(AssertionIndex int32) ([]byte, error)
func (obj *C2PASigner) SetAssertionData(AssertionIndex int32, value []byte) error

Default Value

""

Remarks

The assertion payload.

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

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

The AssertionIndex parameter specifies the index of the item in the array. The size of the array is controlled by the AssertionCount property.

Data Type

[]byte

AssertionMediaType Property (C2PASigner Component)

The media type of the assertion payload.

Syntax

func (obj *C2PASigner) AssertionMediaType(AssertionIndex int32) (string, error)
func (obj *C2PASigner) SetAssertionMediaType(AssertionIndex int32, value string) error

Default Value

"application/cbor"

Remarks

The media type of the assertion payload.

This field holds the media type of AssertionData, 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 AssertionIndex parameter specifies the index of the item in the array. The size of the array is controlled by the AssertionCount property.

Data Type

string

ClaimGenerator Property (C2PASigner Component)

The identifier of the tool that created the claim.

Syntax

func (obj *C2PASigner) ClaimGenerator() (string, error)
func (obj *C2PASigner) SetClaimGenerator(value string) error

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 component records its own name and version.

Data Type

string

IngredientCount Property (C2PASigner Component)

The number of records in the Ingredient arrays.

Syntax

func (obj *C2PASigner) IngredientCount() (int32, error)
func (obj *C2PASigner) SetIngredientCount(value int32) error

Default Value

0

Remarks

This property controls the size of the following arrays:

• IngredientFormat
• IngredientInstanceId
• IngredientManifestLabel
• IngredientRelationship
• IngredientTitle

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

Data Type

int32

IngredientFormat Property (C2PASigner Component)

The media type of the ingredient asset.

Syntax

func (obj *C2PASigner) IngredientFormat(IngredientIndex int32) (string, error)
func (obj *C2PASigner) SetIngredientFormat(IngredientIndex int32, value string) error

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 component fills it in from the source asset when the ingredient is added.

The IngredientIndex parameter specifies the index of the item in the array. The size of the array is controlled by the IngredientCount property.

Data Type

string

IngredientInstanceId Property (C2PASigner Component)

The instance identifier of the ingredient asset.

Syntax

func (obj *C2PASigner) IngredientInstanceId(IngredientIndex int32) (string, error)
func (obj *C2PASigner) SetIngredientInstanceId(IngredientIndex int32, value string) error

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 component 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 component writes, removed it, so there is no corresponding field.

The IngredientIndex parameter specifies the index of the item in the array. The size of the array is controlled by the IngredientCount property.

Data Type

string

IngredientManifestLabel Property (C2PASigner Component)

The label of the ingredient's own C2PA Manifest.

Syntax

func (obj *C2PASigner) IngredientManifestLabel(IngredientIndex int32) (string, error)
func (obj *C2PASigner) SetIngredientManifestLabel(IngredientIndex int32, value string) error

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 IngredientIndex parameter specifies the index of the item in the array. The size of the array is controlled by the IngredientCount property.

Data Type

string

IngredientRelationship Property (C2PASigner Component)

How the ingredient relates to the asset.

Syntax

func (obj *C2PASigner) IngredientRelationship(IngredientIndex int32) (string, error)
func (obj *C2PASigner) SetIngredientRelationship(IngredientIndex int32, value string) error

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 IngredientIndex parameter specifies the index of the item in the array. The size of the array is controlled by the IngredientCount property.

Data Type

string

IngredientTitle Property (C2PASigner Component)

A human-readable name for the ingredient.

Syntax

func (obj *C2PASigner) IngredientTitle(IngredientIndex int32) (string, error)
func (obj *C2PASigner) SetIngredientTitle(IngredientIndex int32, value string) error

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 IngredientIndex parameter specifies the index of the item in the array. The size of the array is controlled by the IngredientCount property.

Data Type

string

InputData Property (C2PASigner Component)

The asset to process, held in memory.

Syntax

func (obj *C2PASigner) InputData() ([]byte, error)
func (obj *C2PASigner) SetInputData(value []byte) error

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 InputFile and this property are set, InputFile takes precedence.

Data Type

[]byte

InputFile Property (C2PASigner Component)

The asset to process.

Syntax

func (obj *C2PASigner) InputFile() (string, error)
func (obj *C2PASigner) SetInputFile(value string) error

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 InputData are set, this property takes precedence.

Data Type

string

OutputData Property (C2PASigner Component)

The signed asset, held in memory.

Syntax

func (obj *C2PASigner) OutputData() ([]byte, error)

Default Value

""

Remarks

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

This property is read-only.

Data Type

[]byte

OutputFile Property (C2PASigner Component)

The file to write the signed asset to.

Syntax

func (obj *C2PASigner) OutputFile() (string, error)
func (obj *C2PASigner) SetOutputFile(value string) error

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 OutputData instead.

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

Data Type

string

Overwrite Property (C2PASigner Component)

Whether the class may overwrite an existing output file.

Syntax

func (obj *C2PASigner) Overwrite() (bool, error)
func (obj *C2PASigner) SetOverwrite(value bool) error

Default Value

false

Remarks

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

The default value is False.

Data Type

bool

SignatureAlgorithm Property (C2PASigner Component)

The algorithm used to sign the claim.

Syntax

func (obj *C2PASigner) SignatureAlgorithm() (string, error)
func (obj *C2PASigner) SetSignatureAlgorithm(value string) error

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 SigningCert. The default value is ES256.

Data Type

string

SigningCertEffectiveDate Property (C2PASigner Component)

The date on which this certificate becomes valid.

Syntax

func (obj *C2PASigner) SigningCertEffectiveDate() (string, error)

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.

Data Type

string

SigningCertExpirationDate Property (C2PASigner Component)

The date on which the certificate expires.

Syntax

func (obj *C2PASigner) SigningCertExpirationDate() (string, error)

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.

Data Type

string

SigningCertExtendedKeyUsage Property (C2PASigner Component)

A comma-delimited list of extended key usage identifiers.

Syntax

func (obj *C2PASigner) SigningCertExtendedKeyUsage() (string, error)

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.

Data Type

string

SigningCertFingerprint Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertFingerprint() (string, error)

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.

Data Type

string

SigningCertFingerprintSHA1 Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertFingerprintSHA1() (string, error)

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.

Data Type

string

SigningCertFingerprintSHA256 Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertFingerprintSHA256() (string, error)

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.

Data Type

string

SigningCertIssuer Property (C2PASigner Component)

The issuer of the certificate.

Syntax

func (obj *C2PASigner) SigningCertIssuer() (string, error)

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.

Data Type

string

SigningCertPrivateKey Property (C2PASigner Component)

The private key of the certificate (if available).

Syntax

func (obj *C2PASigner) SigningCertPrivateKey() (string, error)

Default Value

""

Remarks

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

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

This property is read-only.

Data Type

string

SigningCertPrivateKeyAvailable Property (C2PASigner Component)

Whether a PrivateKey is available for the selected certificate.

Syntax

func (obj *C2PASigner) SigningCertPrivateKeyAvailable() (bool, error)

Default Value

false

Remarks

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

This property is read-only.

Data Type

bool

SigningCertPrivateKeyContainer Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertPrivateKeyContainer() (string, error)

Default Value

""

Remarks

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

This property is read-only.

Data Type

string

SigningCertPublicKey Property (C2PASigner Component)

The public key of the certificate.

Syntax

func (obj *C2PASigner) SigningCertPublicKey() (string, error)

Default Value

""

Remarks

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

This property is read-only.

Data Type

string

SigningCertPublicKeyAlgorithm Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertPublicKeyAlgorithm() (string, error)

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.

Data Type

string

SigningCertPublicKeyLength Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertPublicKeyLength() (int32, error)

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.

Data Type

int32

SigningCertSerialNumber Property (C2PASigner Component)

The serial number of the certificate encoded as a string.

Syntax

func (obj *C2PASigner) SigningCertSerialNumber() (string, error)

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.

Data Type

string

SigningCertSignatureAlgorithm Property (C2PASigner Component)

The text description of the certificate's signature algorithm.

Syntax

func (obj *C2PASigner) SigningCertSignatureAlgorithm() (string, error)

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.

Data Type

string

SigningCertStore Property (C2PASigner Component)

The name of the certificate store for the client certificate.

Syntax

func (obj *C2PASigner) SigningCertStore() ([]byte, error)
func (obj *C2PASigner) SetSigningCertStore(value []byte) error

Default Value

"MY"

Remarks

The name of the certificate store for the client certificate.

The SigningCertStoreType property denotes the type of the certificate store specified by SigningCertStore. If the store is password-protected, specify the password in SigningCertStorePassword.

SigningCertStore is used in conjunction with the SigningCertSubject property to specify client certificates. If SigningCertStore has a value, and SigningCertSubject or SigningCertEncoded is set, a search for a certificate is initiated. Please see the SigningCertSubject 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).

Data Type

[]byte

SigningCertStorePassword Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertStorePassword() (string, error)
func (obj *C2PASigner) SetSigningCertStorePassword(value string) error

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.

Data Type

string

SigningCertStoreType Property (C2PASigner Component)

The type of certificate store for this certificate.

Syntax

func (obj *C2PASigner) SigningCertStoreType() (int32, error)
func (obj *C2PASigner) SetSigningCertStoreType(value int32) error

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

Data Type

int32

SigningCertSubjectAltNames Property (C2PASigner Component)

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

Syntax

func (obj *C2PASigner) SigningCertSubjectAltNames() (string, error)

Default Value

""

Remarks

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

This property is read-only.

Data Type

string

SigningCertThumbprintMD5 Property (C2PASigner Component)

The MD5 hash of the certificate.

Syntax

func (obj *C2PASigner) SigningCertThumbprintMD5() (string, error)

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.

Data Type

string

SigningCertThumbprintSHA1 Property (C2PASigner Component)

The SHA-1 hash of the certificate.

Syntax

func (obj *C2PASigner) SigningCertThumbprintSHA1() (string, error)

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.

Data Type

string

SigningCertThumbprintSHA256 Property (C2PASigner Component)

The SHA-256 hash of the certificate.

Syntax

func (obj *C2PASigner) SigningCertThumbprintSHA256() (string, error)

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.

Data Type

string

SigningCertUsage Property (C2PASigner Component)

The text description of UsageFlags .

Syntax

func (obj *C2PASigner) SigningCertUsage() (string, error)

Default Value

""

Remarks

The text description of SigningCertUsageFlags.

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.

Data Type

string

SigningCertUsageFlags Property (C2PASigner Component)

The flags that show intended use for the certificate.

Syntax

func (obj *C2PASigner) SigningCertUsageFlags() (int32, error)

Default Value

0

Remarks

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

Please see the SigningCertUsage property for a text representation of SigningCertUsageFlags.

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

This property is read-only.

Data Type

int32

SigningCertVersion Property (C2PASigner Component)

The certificate's version number.

Syntax

func (obj *C2PASigner) SigningCertVersion() (string, error)

Default Value

""

Remarks

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

This property is read-only.

Data Type

string

SigningCertSubject Property (C2PASigner Component)

The subject of the certificate used for client authentication.

Syntax

func (obj *C2PASigner) SigningCertSubject() (string, error)
func (obj *C2PASigner) SetSigningCertSubject(value string) error

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.

Data Type

string

SigningCertEncoded Property (C2PASigner Component)

The certificate (PEM/Base64 encoded).

Syntax

func (obj *C2PASigner) SigningCertEncoded() ([]byte, error)
func (obj *C2PASigner) SetSigningCertEncoded(value []byte) error

Default Value

""

Remarks

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

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

Data Type

[]byte

TSAURL Property (C2PASigner Component)

The address of an RFC 3161 Time Stamping Authority.

Syntax

func (obj *C2PASigner) TSAURL() (string, error)
func (obj *C2PASigner) SetTSAURL(value string) error

Default Value

""

Remarks

This property specifies the Time Stamping Authority contacted during signing. When it is set, the component 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.

Data Type

string

AddAction Method (C2PASigner Component)

Records an action in the C2PA Manifest.

Syntax

func (obj *C2PASigner) AddAction(Action string, DigitalSourceType string, SoftwareAgent string) error

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.

DigitalSourceType 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.

SoftwareAgent 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");

AddAssertion Method (C2PASigner Component)

Appends an assertion to the Assertions collection.

Syntax

func (obj *C2PASigner) AddAssertion(AssertionLabel string, MediaType string, Data []byte) error

Remarks

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

AssertionLabel is the C2PA assertion label, such as stds.schema-org.CreativeWork or stds.exif. MediaType 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 component.

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

AddIngredient Method (C2PASigner Component)

Records that an asset went into the one being signed.

Syntax

func (obj *C2PASigner) AddIngredient(SourceFile string, Title string, Relationship string) error

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 (C2PASigner Component)

Sets or retrieves a configuration setting.

Syntax

func (obj *C2PASigner) Config(ConfigurationString string) (string, error)

Remarks

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

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the component, 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 (C2PASigner Component)

This method will reset the class.

Syntax

func (obj *C2PASigner) Reset() error

Remarks

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

Sign Method (C2PASigner Component)

Builds, signs, and embeds a C2PA Manifest.

Syntax

func (obj *C2PASigner) Sign() error

Remarks

This method reads the asset named by InputFile (or held in InputData), builds a C2PA Manifest from the Assertions properties, signs the claim with SigningCert, embeds the manifest into the asset, and writes the result to OutputFile (or OutputData).

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 SigningCert has no private key, when SignatureAlgorithm is incompatible with that key, or when the input asset is of a format the component cannot embed into.

Error Event (C2PASigner Component)

Fired when information is available about errors during data delivery.

Syntax

// C2PASignerErrorEventArgs carries the C2PASigner Error event's parameters.
type C2PASignerErrorEventArgs struct {...}

func (args *C2PASignerErrorEventArgs) ErrorCode() int32
func (args *C2PASignerErrorEventArgs) Description() string

// C2PASignerErrorEvent defines the signature of the C2PASigner Error event's handler function.
type C2PASignerErrorEvent func(sender *C2PASigner, args *C2PASignerErrorEventArgs)

func (obj *C2PASigner) GetOnErrorHandler() C2PASignerErrorEvent
func (obj *C2PASigner) SetOnErrorHandler(handlerFunc C2PASignerErrorEvent)

Remarks

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

The ErrorCode 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.

Log Event (C2PASigner Component)

This event fires once for each log message.

Syntax

// C2PASignerLogEventArgs carries the C2PASigner Log event's parameters.
type C2PASignerLogEventArgs struct {...}

func (args *C2PASignerLogEventArgs) LogLevel() int32
func (args *C2PASignerLogEventArgs) Message() string
func (args *C2PASignerLogEventArgs) LogType() string

// C2PASignerLogEvent defines the signature of the C2PASigner Log event's handler function.
type C2PASignerLogEvent func(sender *C2PASigner, args *C2PASignerLogEventArgs)

func (obj *C2PASigner) GetOnLogHandler() C2PASignerLogEvent
func (obj *C2PASigner) SetOnLogHandler(handlerFunc C2PASignerLogEvent)

Remarks

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

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

Message is the log entry.

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

Config Settings (C2PASigner Component)

The component 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 component, access to these internal properties is provided through the Config method.

C2PASigner Config Settings

Base Config Settings

Trappable Errors (C2PASigner Component)

C2PASigner Errors