C2PAVerifier Control

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Extracts and validates the C2PA Manifests embedded in an asset.

Syntax

C2PAVerifier

Remarks

The C2PAVerifier control reads the Content Credentials embedded in an asset and reports what can be established about them: whether the signature is intact, whether the signer is trusted, and whether the asset bytes still match what was signed.

Supported Formats

JPEG, PNG and PDF are supported. The format is detected from the asset itself, and an asset in any other format is refused rather than reported as carrying no provenance, since those are different answers.

The PDF reader locates the manifest by its file specification's AFRelationship, so it reads manifests written by any conforming tool, not only those this product produced.

Validating an Asset

Set InputFile to the asset and call Verify. Every manifest found is then added to the Manifests properties, and one entry per check performed is added to ValidationResults.

C2PAVerifier verifier = new C2PAVerifier(); verifier.InputFile = "photo-signed.jpg"; verifier.Verify(); foreach (C2PAValidationResult result in verifier.ValidationResults) Console.WriteLine(result.Severity + " " + result.Code + ": " + result.Explanation);

Reading the Results

Validation is not a single boolean. The C2PA specification defines a status code for each individual check, and the control reports them verbatim so an application can decide how much weight to give each one. A signature that verifies but whose signer is not on a trust list is a different situation from one whose content binding fails.

Each entry in ValidationResults carries a Severity of success, informational, or failure. Codes such as claimSignature.validated and assertion.dataHash.match are successes; assertion.dataHash.mismatch means the asset was altered after signing; signingCredential.untrusted means the signature is intact but the signer does not chain to any configured trust anchor.

The ValidationStatus event fires once for each result as it is produced, which is convenient when validation should be reported incrementally rather than inspected afterwards.

The Provenance Chain

An asset may carry more than one manifest: the active manifest describes the most recent edit, and earlier manifests describe the ingredients it was built from. All of them appear in Manifests, with ActiveManifestIndex identifying the active one.

verifier.Verify(); C2PAManifest active = verifier.Manifests[verifier.ActiveManifestIndex]; Console.WriteLine("Produced by " + active.ClaimGenerator + ", signed by " + active.SignerSubject);

Trust Anchors

By default the control validates signing certificates against the built-in C2PA trust list. Additional anchors are supplied through the TrustedCerts properties, and are used in addition to the built-in list rather than instead of it, as the C2PA specification prescribes. Setting UseC2PATrustList to False restricts validation to the supplied anchors alone, which is the correct configuration for a private PKI.

Setting CheckRevocation to True additionally performs online revocation checking. Revocation information stapled into the manifest by the signer is always used when present, whether or not online checking is enabled.

Property List

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

ActiveManifestIndex Property (C2PAVerifier Control)

The index of the active manifest in the Manifests collection.

Syntax

c2paverifiercontrol.ActiveManifestIndex

Default Value

-1

Remarks

This property identifies which item in Manifests is the active manifest, the one describing how the asset reached its current state. The C2PA specification fixes the active manifest as the last one in the manifest store.

The value is -1 when no manifest was found.

This property is read-only and not available at design time.

Data Type

Integer

CheckRevocation Property (C2PAVerifier Control)

Whether online revocation checking is performed.

Syntax

c2paverifiercontrol.CheckRevocation[=boolean]

Default Value

False

Remarks

This property controls whether the control contacts OCSP responders or downloads CRLs to determine whether the signing certificate has been revoked.

Revocation information stapled into the manifest by the signer is always used when present, whether or not this property is set. Setting it to True additionally performs an online check, which requires network access and makes verification slower.

When revocation cannot be determined, verification does not fail; an informational result such as signingCredential.ocsp.inaccessible or signingCredential.ocsp.skipped is reported so the application can decide what that is worth.

The default value is False.

This property is not available at design time.

Data Type

Boolean

IngredientCount Property (C2PAVerifier Control)

The number of records in the Ingredient arrays.

Syntax

c2paverifiercontrol.IngredientCount[=integer]

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.

This property is not available at design time.

Data Type

Integer

IngredientFormat Property (C2PAVerifier Control)

The media type of the ingredient asset.

Syntax

c2paverifiercontrol.IngredientFormat(IngredientIndex)[=string]

Default Value

""

Remarks

The media type of the ingredient asset.

This property holds the media type of the asset that went into this one, for example image/jpeg, image/png or application/pdf. The control 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.

This property is not available at design time.

Data Type

String

IngredientInstanceId Property (C2PAVerifier Control)

The instance identifier of the ingredient asset.

Syntax

c2paverifiercontrol.IngredientInstanceId(IngredientIndex)[=string]

Default Value

""

Remarks

The instance identifier of the ingredient asset.

This property 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 control 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 control writes, removed it, so there is no corresponding property.

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

This property is not available at design time.

Data Type

String

IngredientManifestLabel Property (C2PAVerifier Control)

The label of the ingredient's own C2PA Manifest.

Syntax

c2paverifiercontrol.IngredientManifestLabel(IngredientIndex)[=string]

Default Value

""

Remarks

The label of the ingredient's own C2PA Manifest.

This property 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.

This property is not available at design time.

Data Type

String

IngredientRelationship Property (C2PAVerifier Control)

How the ingredient relates to the asset.

Syntax

c2paverifiercontrol.IngredientRelationship(IngredientIndex)[=string]

Default Value

"componentOf"

Remarks

How the ingredient relates to the asset.

This property 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.

This property is not available at design time.

Data Type

String

IngredientTitle Property (C2PAVerifier Control)

A human-readable name for the ingredient.

Syntax

c2paverifiercontrol.IngredientTitle(IngredientIndex)[=string]

Default Value

""

Remarks

A human-readable name for the ingredient.

This property 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.

This property is not available at design time.

Data Type

String

InputData Property (C2PAVerifier Control)

The asset to process, held in memory.

Syntax

c2paverifiercontrol.InputData[=string]

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.

To read or write binary data to the property, a Variant (Byte Array) version is provided in .InputDataB.

Data Type

Binary String

InputFile Property (C2PAVerifier Control)

The asset to process.

Syntax

c2paverifiercontrol.InputFile[=string]

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

ManifestCount Property (C2PAVerifier Control)

The number of records in the Manifest arrays.

Syntax

c2paverifiercontrol.ManifestCount

Default Value

0

Remarks

This property controls the size of the following arrays:

• ManifestClaimGenerator
• ManifestIsActive
• ManifestLabel
• ManifestSignerSubject
• ManifestSigningTime

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

This property is read-only and not available at design time.

Data Type

Integer

ManifestClaimGenerator Property (C2PAVerifier Control)

The tool that produced this manifest.

Syntax

c2paverifiercontrol.ManifestClaimGenerator(ManifestIndex)

Default Value

""

Remarks

The tool that produced this manifest.

This property names the application that created the claim, as recorded by its signer.

It is a claim, not a verified fact: it says what the signer wrote down. What the signature establishes is who wrote it, which is ManifestSignerSubject.

The ManifestIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ManifestCount property.

This property is read-only and not available at design time.

Data Type

String

ManifestIsActive Property (C2PAVerifier Control)

Whether this is the active manifest.

Syntax

c2paverifiercontrol.ManifestIsActive(ManifestIndex)

Default Value

False

Remarks

Whether this is the active manifest.

This property is True for the manifest that describes how the asset reached its current state, and False for the manifests that came with its ingredients.

The C2PA specification fixes the active manifest as the last one in the manifest store.

The ManifestIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ManifestCount property.

This property is read-only and not available at design time.

Data Type

Boolean

ManifestLabel Property (C2PAVerifier Control)

The manifest's identifier.

Syntax

c2paverifiercontrol.ManifestLabel(ManifestIndex)

Default Value

""

Remarks

The manifest's identifier.

This property holds the manifest's label, a urn:c2pa value that uniquely identifies it within the manifest store. Ingredients refer to their manifests by this value.

The ManifestIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ManifestCount property.

This property is read-only and not available at design time.

Data Type

String

ManifestSignerSubject Property (C2PAVerifier Control)

The subject of the certificate that signed the claim.

Syntax

c2paverifiercontrol.ManifestSignerSubject(ManifestIndex)

Default Value

""

Remarks

The subject of the certificate that signed the claim.

This property holds the distinguished name of the signing certificate's subject.

This is the identity the signature actually establishes, provided the certificate chains to a trust anchor. Check the validation results for signingCredential.trusted before treating it as meaningful: an untrusted certificate can carry any subject its issuer chose to put in it.

The ManifestIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ManifestCount property.

This property is read-only and not available at design time.

Data Type

String

ManifestSigningTime Property (C2PAVerifier Control)

When the claim was signed.

Syntax

c2paverifiercontrol.ManifestSigningTime(ManifestIndex)

Default Value

""

Remarks

When the claim was signed.

This property holds the signing time as an RFC 3339 date and time.

When the manifest carries an RFC 3161 time-stamp, this is the time attested by the Time Stamping Authority, and it is what allows the signature to remain verifiable after the signing certificate expires. Without a time-stamp the value is the signer's own claimed time, which carries no more weight than the rest of the claim.

The ManifestIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ManifestCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertCount Property (C2PAVerifier Control)

The number of records in the TrustedCert arrays.

Syntax

c2paverifiercontrol.TrustedCertCount[=integer]

Default Value

0

Remarks

This property controls the size of the following arrays:

• TrustedCertEffectiveDate
• TrustedCertEncoded
• TrustedCertExpirationDate
• TrustedCertExtendedKeyUsage
• TrustedCertFingerprint
• TrustedCertFingerprintSHA1
• TrustedCertFingerprintSHA256
• TrustedCertIssuer
• TrustedCertPrivateKey
• TrustedCertPrivateKeyAvailable
• TrustedCertPrivateKeyContainer
• TrustedCertPublicKey
• TrustedCertPublicKeyAlgorithm
• TrustedCertPublicKeyLength
• TrustedCertSerialNumber
• TrustedCertSignatureAlgorithm
• TrustedCertStore
• TrustedCertStorePassword
• TrustedCertStoreType
• TrustedCertSubject
• TrustedCertSubjectAltNames
• TrustedCertThumbprintMD5
• TrustedCertThumbprintSHA1
• TrustedCertThumbprintSHA256
• TrustedCertUsage
• TrustedCertUsageFlags
• TrustedCertVersion

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

This property is not available at design time.

Data Type

Integer

TrustedCertEffectiveDate Property (C2PAVerifier Control)

The date on which this certificate becomes valid.

Syntax

c2paverifiercontrol.TrustedCertEffectiveDate(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertExpirationDate Property (C2PAVerifier Control)

The date on which the certificate expires.

Syntax

c2paverifiercontrol.TrustedCertExpirationDate(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertExtendedKeyUsage Property (C2PAVerifier Control)

A comma-delimited list of extended key usage identifiers.

Syntax

c2paverifiercontrol.TrustedCertExtendedKeyUsage(TrustedCertIndex)

Default Value

""

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertFingerprint Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertFingerprint(TrustedCertIndex)

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertFingerprintSHA1 Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertFingerprintSHA1(TrustedCertIndex)

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertFingerprintSHA256 Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertFingerprintSHA256(TrustedCertIndex)

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertIssuer Property (C2PAVerifier Control)

The issuer of the certificate.

Syntax

c2paverifiercontrol.TrustedCertIssuer(TrustedCertIndex)

Default Value

""

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertPrivateKey Property (C2PAVerifier Control)

The private key of the certificate (if available).

Syntax

c2paverifiercontrol.TrustedCertPrivateKey(TrustedCertIndex)

Default Value

""

Remarks

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

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertPrivateKeyAvailable Property (C2PAVerifier Control)

Whether a PrivateKey is available for the selected certificate.

Syntax

c2paverifiercontrol.TrustedCertPrivateKeyAvailable(TrustedCertIndex)

Default Value

False

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

Boolean

TrustedCertPrivateKeyContainer Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertPrivateKeyContainer(TrustedCertIndex)

Default Value

""

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertPublicKey Property (C2PAVerifier Control)

The public key of the certificate.

Syntax

c2paverifiercontrol.TrustedCertPublicKey(TrustedCertIndex)

Default Value

""

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertPublicKeyAlgorithm Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertPublicKeyAlgorithm(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertPublicKeyLength Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertPublicKeyLength(TrustedCertIndex)

Default Value

0

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

Integer

TrustedCertSerialNumber Property (C2PAVerifier Control)

The serial number of the certificate encoded as a string.

Syntax

c2paverifiercontrol.TrustedCertSerialNumber(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertSignatureAlgorithm Property (C2PAVerifier Control)

The text description of the certificate's signature algorithm.

Syntax

c2paverifiercontrol.TrustedCertSignatureAlgorithm(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertStore Property (C2PAVerifier Control)

The name of the certificate store for the client certificate.

Syntax

c2paverifiercontrol.TrustedCertStore(TrustedCertIndex)[=string]

Default Value

"MY"

Remarks

The name of the certificate store for the client certificate.

The TrustedCertStoreType property denotes the type of the certificate store specified by TrustedCertStore. If the store is password-protected, specify the password in TrustedCertStorePassword.

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

To read or write binary data to the property, a Variant (Byte Array) version is provided in .TrustedCertStoreB.

This property is not available at design time.

Data Type

Binary String

TrustedCertStorePassword Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertStorePassword(TrustedCertIndex)[=string]

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is not available at design time.

Data Type

String

TrustedCertStoreType Property (C2PAVerifier Control)

The type of certificate store for this certificate.

Syntax

c2paverifiercontrol.TrustedCertStoreType(TrustedCertIndex)[=integer]

Possible Values

cstUser(0), cstMachine(1), cstPFXFile(2), cstPFXBlob(3), cstJKSFile(4), cstJKSBlob(5), cstPEMKeyFile(6), cstPEMKeyBlob(7), cstPublicKeyFile(8), cstPublicKeyBlob(9), cstSSHPublicKeyBlob(10), cstP7BFile(11), cstP7BBlob(12), cstSSHPublicKeyFile(13), cstPPKFile(14), cstPPKBlob(15), cstXMLFile(16), cstXMLBlob(17), cstJWKFile(18), cstJWKBlob(19), cstSecurityKey(20), cstBCFKSFile(21), cstBCFKSBlob(22), cstPKCS11(23), cstAuto(99)

Default Value

0

Remarks

The type of certificate store for this certificate.

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is not available at design time.

Data Type

Integer

TrustedCertSubjectAltNames Property (C2PAVerifier Control)

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

Syntax

c2paverifiercontrol.TrustedCertSubjectAltNames(TrustedCertIndex)

Default Value

""

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertThumbprintMD5 Property (C2PAVerifier Control)

The MD5 hash of the certificate.

Syntax

c2paverifiercontrol.TrustedCertThumbprintMD5(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertThumbprintSHA1 Property (C2PAVerifier Control)

The SHA-1 hash of the certificate.

Syntax

c2paverifiercontrol.TrustedCertThumbprintSHA1(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertThumbprintSHA256 Property (C2PAVerifier Control)

The SHA-256 hash of the certificate.

Syntax

c2paverifiercontrol.TrustedCertThumbprintSHA256(TrustedCertIndex)

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertUsage Property (C2PAVerifier Control)

The text description of UsageFlags .

Syntax

c2paverifiercontrol.TrustedCertUsage(TrustedCertIndex)

Default Value

""

Remarks

The text description of TrustedCertUsageFlags.

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.

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertUsageFlags Property (C2PAVerifier Control)

The flags that show intended use for the certificate.

Syntax

c2paverifiercontrol.TrustedCertUsageFlags(TrustedCertIndex)

Default Value

0

Remarks

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

Please see the TrustedCertUsage property for a text representation of TrustedCertUsageFlags.

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

Integer

TrustedCertVersion Property (C2PAVerifier Control)

The certificate's version number.

Syntax

c2paverifiercontrol.TrustedCertVersion(TrustedCertIndex)

Default Value

""

Remarks

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is read-only and not available at design time.

Data Type

String

TrustedCertSubject Property (C2PAVerifier Control)

The subject of the certificate used for client authentication.

Syntax

c2paverifiercontrol.TrustedCertSubject(TrustedCertIndex)[=string]

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 properties and values. For instance, "CN=www.server.com, OU=test, C=US, E=example@email.com". Common properties and their meanings are as follows:

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

This property is not available at design time.

Data Type

String

TrustedCertEncoded Property (C2PAVerifier Control)

The certificate (PEM/Base64 encoded).

Syntax

c2paverifiercontrol.TrustedCertEncoded(TrustedCertIndex)[=string]

Default Value

""

Remarks

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

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

The TrustedCertIndex parameter specifies the index of the item in the array. The size of the array is controlled by the TrustedCertCount property.

To read or write binary data to the property, a Variant (Byte Array) version is provided in .TrustedCertEncodedB.

This property is not available at design time.

Data Type

Binary String

UseC2PATrustList Property (C2PAVerifier Control)

Whether the built-in C2PA trust list is used.

Syntax

c2paverifiercontrol.UseC2PATrustList[=boolean]

Default Value

True

Remarks

This property controls whether signing certificates are validated against the C2PA trust list built into the control, in addition to any anchors in TrustedCerts.

The default value is True, which is the configuration the C2PA specification describes for a validator: the trust anchors for the claim signing extended key usage include the C2PA trust list, and a user may configure further anchors on top of it.

Set this property to False to validate against TrustedCerts alone, which is appropriate for a private PKI where the public list has no bearing.

The built-in list is a snapshot taken when the control was built. Query the TrustListVersion and TrustListDate configuration settings to determine how current that snapshot is; supply newer anchors through TrustedCerts when it has aged.

This property is not available at design time.

Data Type

Boolean

ValidationResultCount Property (C2PAVerifier Control)

The number of records in the ValidationResult arrays.

Syntax

c2paverifiercontrol.ValidationResultCount

Default Value

0

Remarks

This property controls the size of the following arrays:

• ValidationResultCode
• ValidationResultExplanation
• ValidationResultManifestLabel
• ValidationResultSeverity

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

This property is read-only and not available at design time.

Data Type

Integer

ValidationResultCode Property (C2PAVerifier Control)

The C2PA status code.

Syntax

c2paverifiercontrol.ValidationResultCode(ValidationResultIndex)

Default Value

""

Remarks

The C2PA status code.

This property holds the status code defined by the C2PA specification, reported verbatim so it can be matched against the specification or passed to another conforming implementation.

Frequently encountered values are:

The ValidationResultIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ValidationResultCount property.

This property is read-only and not available at design time.

Data Type

String

ValidationResultExplanation Property (C2PAVerifier Control)

A human-readable description of the result.

Syntax

c2paverifiercontrol.ValidationResultExplanation(ValidationResultIndex)

Default Value

""

Remarks

A human-readable description of the result.

This property describes what was checked and what was found, in text suitable for showing to a person or writing to a log.

Application logic should branch on ValidationResultCode rather than on this text, which is not part of the C2PA specification and may be reworded.

The ValidationResultIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ValidationResultCount property.

This property is read-only and not available at design time.

Data Type

String

ValidationResultManifestLabel Property (C2PAVerifier Control)

The manifest the result applies to.

Syntax

c2paverifiercontrol.ValidationResultManifestLabel(ValidationResultIndex)

Default Value

""

Remarks

The manifest the result applies to.

This property holds the urn:c2pa label of the manifest that was being checked, so results can be attributed correctly when an asset carries a chain of them.

The ValidationResultIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ValidationResultCount property.

This property is read-only and not available at design time.

Data Type

String

ValidationResultSeverity Property (C2PAVerifier Control)

How serious the result is.

Syntax

c2paverifiercontrol.ValidationResultSeverity(ValidationResultIndex)

Default Value

0

Remarks

How serious the result is.

This property classifies the result:

An asset should be treated as validated only when no result carries a severity of 2 and the successes cover the checks the application requires.

The ValidationResultIndex parameter specifies the index of the item in the array. The size of the array is controlled by the ValidationResultCount property.

This property is read-only and not available at design time.

Data Type

Integer

Config Method (C2PAVerifier Control)

Sets or retrieves a configuration setting.

Syntax

c2paverifiercontrol.Config ConfigurationString

Remarks

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

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the control, 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 (C2PAVerifier Control)

This method will reset the control.

Syntax

c2paverifiercontrol.Reset 

Remarks

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

Verify Method (C2PAVerifier Control)

Extracts and validates the C2PA Manifests in the asset.

Syntax

c2paverifiercontrol.Verify 

Remarks

This method reads the asset named by InputFile (or held in InputData), locates the C2PA Manifest Store, and validates it. Manifests and ValidationResults are populated when it returns.

For the active manifest, the control verifies the claim signature, builds a certificate path from the signing certificate to the active trust anchors, and recomputes the content binding hash over the asset to confirm the bytes still match what was signed.

C2PAVerifier verifier = new C2PAVerifier(); verifier.InputFile = "photo-signed.jpg"; verifier.Verify(); foreach (C2PAValidationResult result in verifier.ValidationResults) Console.WriteLine(result.Severity + " " + result.Code + ": " + result.Explanation);

A failed check does not throw. It is reported through ValidationResults and the ValidationStatus event, so that a partially trustworthy asset can be described accurately rather than merely rejected. An error is thrown only when the asset cannot be read at all, or carries no C2PA Manifest.

Error Event (C2PAVerifier Control)

Fired when information is available about errors during data delivery.

Syntax

Sub c2paverifiercontrol_Error(ErrorCode As Integer, Description As String)

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally the control 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 (C2PAVerifier Control)

This event fires once for each log message.

Syntax

Sub c2paverifiercontrol_Log(LogLevel As Integer, Message As String, LogType As String)

Remarks

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

ManifestFound Event (C2PAVerifier Control)

Fires once for each C2PA Manifest found in the asset.

Syntax

Sub c2paverifiercontrol_ManifestFound(ManifestLabel As String, ClaimGenerator As String, SignerSubject As String, IsActive As Boolean)

Remarks

This event fires as each manifest is located, before validation of that manifest completes.

ManifestLabel is the manifest's identifier, a urn:c2pa value. ClaimGenerator names the tool that produced it. SignerSubject is the subject of the certificate that signed the claim. IsActive is True for the active manifest, which is the last one in the store.

The same information is available afterwards through the Manifests properties; this event is for applications that would rather report provenance as it is discovered.

ValidationStatus Event (C2PAVerifier Control)

Fires once for each validation status code produced.

Syntax

Sub c2paverifiercontrol_ValidationStatus(Code As String, Explanation As String, Severity As Integer, ManifestLabel As String)

Remarks

This event fires as each check completes, giving the same information that is appended to ValidationResults.

Code is the status code defined by the C2PA specification, reported verbatim. Common values are claimSignature.validated and assertion.dataHash.match on success, assertion.dataHash.mismatch when the asset was altered after signing, and signingCredential.untrusted when the signature is intact but the signer chains to no configured trust anchor.

Explanation is a human-readable description of the check.

Severity is 0 (success), 1 (informational), or 2 (failure).

ManifestLabel identifies which manifest the result applies to.

Config Settings (C2PAVerifier Control)

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

C2PAVerifier Config Settings

Base Config Settings

Trappable Errors (C2PAVerifier Control)

C2PAVerifier Errors