C2PASigner Class

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

Syntax

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 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 class 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 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.

Actions Property (C2PASigner Class)

The actions recorded in the Manifest.

Syntax

public C2PAActionList getActions();

Remarks

Each entry describes something that was done to the content. AddAction is the short way to add one; this collection is how an application reads them back, and how it reaches the When field, which AddAction does not take.

The actions travel in a single c2pa.actions.v2 assertion, written when the Manifest is signed.

Example. Recording when an edit happened:

C2PASigner signer = new C2PASigner(); signer.InputFile = "edited.jpg"; signer.SigningCert = cert; signer.AddAction("c2pa.edited", "", "Acme Editor/3.0"); // AddAction takes no timestamp, so set it on the queued action. signer.Actions[0].When = "2026-09-01T10:30:00Z"; signer.Sign();

Example. Checking what will be recorded before signing:

for (int i = 0; i < signer.Actions.Count; i++) { Console.WriteLine(signer.Actions[i].Action + " by " + signer.Actions[i].SoftwareAgent); }

This property is not available at design time.

Please refer to the C2PAAction type for a complete list of fields.

Assertions Property (C2PASigner Class)

The assertions to record in the C2PA Manifest.

Syntax

public C2PAAssertionList getAssertions();

Remarks

This collection holds the C2PAAssertion items written into the manifest when Sign is called. The AddAssertion and AddAction methods are a convenient way to append items without constructing them directly.

The content binding assertion, which ties the manifest to the asset bytes, is always computed by the class and is not part of this collection. An application cannot supply it, because a self-supplied binding would defeat tamper detection.

This property is not available at design time.

Please refer to the C2PAAssertion type for a complete list of fields.

ClaimGenerator Property (C2PASigner Class)

The identifier of the tool that created the claim.

Syntax

public String getClaimGenerator();
public void setClaimGenerator(String claimGenerator);

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.

This property is not available at design time.

Ingredients Property (C2PASigner Class)

The ingredients recorded in the Manifest.

Syntax

public C2PAIngredientList getIngredients();

Remarks

Each entry is an asset that went into the one being signed, added by AddIngredient. This collection is how an application reads them back before signing.

When an ingredient's source carried a Manifest of its own, ManifestLabel names it and that Manifest is carried in the store being written. When it did not, ManifestLabel is empty: the ingredient records what the source was, and the chain stops there.

Example. Reading back what was recorded:

signer.AddIngredient("original.jpg", "Original photograph", "parentOf"); C2PAIngredient added = signer.Ingredients[0]; Console.WriteLine(added.Title + " (" + added.Format + ") " + added.Relationship); if (added.ManifestLabel.Length > 0) { Console.WriteLine(" its own manifest travels along: " + added.ManifestLabel); } else { Console.WriteLine(" the source carried no manifest; the chain stops here"); }

This property is not available at design time.

Please refer to the C2PAIngredient type for a complete list of fields.

InputData Property (C2PASigner Class)

The asset to process, held in memory.

Syntax

public byte[] getInputData();
public void setInputData(byte[] inputData);

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.

InputFile Property (C2PASigner Class)

The asset to process.

Syntax

public String getInputFile();
public void setInputFile(String inputFile);

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.

OutputData Property (C2PASigner Class)

The signed asset, held in memory.

Syntax

public byte[] getOutputData();

Default Value

""

Remarks

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

This property is read-only.

OutputFile Property (C2PASigner Class)

The file to write the signed asset to.

Syntax

public String getOutputFile();
public void setOutputFile(String outputFile);

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.

Overwrite Property (C2PASigner Class)

Whether the class may overwrite an existing output file.

Syntax

public boolean isOverwrite();
public void setOverwrite(boolean overwrite);

Default Value

False

Remarks

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

The default value is False.

SignatureAlgorithm Property (C2PASigner Class)

The algorithm used to sign the claim.

Syntax

public String getSignatureAlgorithm();
public void setSignatureAlgorithm(String signatureAlgorithm);

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.

This property is not available at design time.

SigningCert Property (C2PASigner Class)

The certificate used to sign the C2PA Manifest.

Syntax

public Certificate getSigningCert();
public void setSigningCert(Certificate signingCert);

Remarks

This property specifies the certificate used to sign the claim. The certificate must have an associated private key.

The C2PA specification requires that a claim signing certificate carry the c2pa-kp-claimSigning extended key usage, OID 1.3.6.1.4.1.62558.2.1. A certificate without it will be rejected by conforming validators even though the signature itself is well formed.

The full chain presented with the certificate is embedded in the signature, so a validator can build a path to its own trust anchors without fetching intermediates.

This property is not available at design time.

Please refer to the Certificate type for a complete list of fields.

TSAURL Property (C2PASigner Class)

The address of an RFC 3161 Time Stamping Authority.

Syntax

public String getTSAURL();
public void setTSAURL(String 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.

This property is not available at design time.

AddAction Method (C2PASigner Class)

Records an action in the C2PA Manifest.

Syntax

public void addAction(String action, String digitalSourceType, String softwareAgent);

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 Class)

Appends an assertion to the Assertions collection.

Syntax

public void addAssertion(String assertionLabel, String mediaType, byte[] data);

Remarks

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

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

AddIngredient Method (C2PASigner Class)

Records that an asset went into the one being signed.

Syntax

public void addIngredient(String sourceFile, String title, String relationship);

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 Class)

Sets or retrieves a configuration setting.

Syntax

public String config(String configurationString);

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 (C2PASigner Class)

This method will reset the class.

Syntax

public void reset();

Remarks

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

Sign Method (C2PASigner Class)

Builds, signs, and embeds a C2PA Manifest.

Syntax

public void sign();

Remarks

This method reads the asset named by InputFile (or held in InputData), builds a C2PA Manifest from the Assertions collection, 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 class cannot embed into.

Error Event (C2PASigner Class)

Fired when information is available about errors during data delivery.

Syntax

public class DefaultC2PASignerEventListener implements C2PASignerEventListener {
  ...
  public void error(C2PASignerErrorEvent e) {}
  ...
}

public class C2PASignerErrorEvent {
  public int errorCode;
  public String description;
}

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally the class throws an exception.

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 Class)

This event fires once for each log message.

Syntax

public class DefaultC2PASignerEventListener implements C2PASignerEventListener {
  ...
  public void log(C2PASignerLogEvent e) {}
  ...
}

public class C2PASignerLogEvent {
  public int logLevel;
  public String message;
  public String logType;
}

Remarks

This event fires once for each log message generated by the class. 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.

C2PAAction Type

A single action recorded in the actions assertion.

Remarks

This type represents one entry in a C2PA Manifest's actions assertion: something that was done to the asset, by what, and what kind of content resulted.

The actions assertion is where an asset's history is written down, and it is the mechanism regulators point to for AI disclosure. An asset produced by a generative model carries a c2pa.created action whose DigitalSourceType identifies the output as trained algorithmic media.

• Action
• DigitalSourceType
• SoftwareAgent
• When

Fields

Constructors

public C2PAAction();

C2PAAssertion Type

A single assertion recorded in a C2PA Manifest.

Remarks

This type represents one assertion: a labelled statement about the asset, stored in the manifest and covered by the claim signature.

Assertions are how a C2PA Manifest says anything at all. Some describe what was done to the asset, some describe who made it, and one, the content binding, ties the manifest to the asset bytes. Each carries a label defined by the C2PA specification and a payload whose shape that label determines.

The payload is exposed as raw data rather than parsed into typed fields, so that assertion types added to the standard after this component was built can still be read and written.

• AssertionLabel
• Data
• MediaType

Fields

Constructors

public C2PAAssertion();

C2PAIngredient Type

An asset that went into the one being described.

Remarks

This type represents an ingredient: another asset that was used to produce this one, together with the relationship between them.

Ingredients are what turn individual manifests into a provenance chain. When an editor opens a photograph and places it into a composite, the composite's manifest records the photograph as an ingredient, carrying that photograph's own manifest with it. A consumer can then walk backwards through the chain to the original capture.

• Format
• InstanceId
• ManifestLabel
• Relationship
• Title

Fields

Constructors

public C2PAIngredient();

Certificate Type

This is the digital certificate being used.

Remarks

This type describes the current digital certificate. The certificate may be a public or private key. The fields are used to identify or select certificates.

• EffectiveDate
• ExpirationDate
• ExtendedKeyUsage
• Fingerprint
• FingerprintSHA1
• FingerprintSHA256
• Issuer
• KeyPassword
• PrivateKey
• PrivateKeyAvailable
• PrivateKeyContainer
• PublicKey
• PublicKeyAlgorithm
• PublicKeyLength
• SerialNumber
• SignatureAlgorithm
• Store
• StorePassword
• StoreType
• SubjectAltNames
• ThumbprintMD5
• ThumbprintSHA1
• ThumbprintSHA256
• Usage
• UsageFlags
• Version
• Subject
• Encoded

Fields

Constructors

public Certificate();

public Certificate(String certificateFile);

public Certificate(byte[] encoded);

public Certificate(int storeType, String store, String storePassword, String subject);

public Certificate(int storeType, String store, String storePassword, String subject, String configurationString);

public Certificate(int storeType, String store, String storePassword, byte[] encoded);

public Certificate(int storeType, byte[] store, String storePassword, String subject);

public Certificate(int storeType, byte[] store, String storePassword, String subject, String configurationString);

public Certificate(int storeType, byte[] store, String storePassword, byte[] encoded);

Config Settings (C2PASigner Class)

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

Trappable Errors (C2PASigner Class)

C2PASigner Errors