IdentityCredential

createEphemeralKeyPair

@NonNull abstract fun createEphemeralKeyPair(): KeyPair

Create an ephemeral key pair to use to establish a secure channel with a reader.

Most applications will use only the public key, and only to send it to the reader, allowing the private key to be used internally for encryptMessageToReader(byte[]) and decryptMessageFromReader(byte[]). The private key is also provided for applications that wish to use a cipher suite that is not supported by IdentityCredentialStore.

decryptMessageFromReader

@NonNull abstract fun decryptMessageFromReader(@NonNull messageCiphertext: ByteArray): ByteArray

Decrypt a message received from the reader.

In order for this to work, setSessionTranscript(byte[]) and setReaderEphemeralPublicKey(PublicKey) must have already been called.

encryptMessageToReader

@NonNull abstract fun encryptMessageToReader(@NonNull messagePlaintext: ByteArray): ByteArray

Encrypt a message for transmission to the reader.

In order for this to work, setSessionTranscript(byte[]) and setReaderEphemeralPublicKey(PublicKey) must have already been called.

getAuthKeysNeedingCertification

@NonNull abstract fun getAuthKeysNeedingCertification(): MutableCollection<X509Certificate!>

Gets a collection of dynamic authentication keys that need certification.

When there aren't enough certified dynamic authentication keys, either because the key count has been increased or because one or more keys have reached their usage count, this method will generate replacement keys and certificates and return them for issuer certification. The issuer certificates and associated static authentication data must then be provided back to the IdentityCredential using storeStaticAuthenticationData(X509Certificate, byte[]).

Each X.509 certificate is signed by CredentialKey. The certificate chain for CredentialKey can be obtained using the getCredentialKeyCertificateChain() method.

getAuthenticationDataUsageCount

@NonNull abstract fun getAuthenticationDataUsageCount(): IntArray

Get the number of times the dynamic authentication keys have been used.

getCredentialKeyCertificateChain

@NonNull abstract fun getCredentialKeyCertificateChain(): MutableCollection<X509Certificate!>

Gets the X.509 certificate chain for the CredentialKey which identifies this credential to the issuing authority. This is the same certificate chain that was returned by WritableIdentityCredential#getCredentialKeyCertificateChain(byte[]) when the credential was first created and its Android Keystore extension will contain the challenge data set at that time. See the documentation for that method for important information about this certificate chain.

getCryptoObject

@Nullable abstract fun getCryptoObject(): BiometricPrompt.CryptoObject?

Gets a BiometricPrompt.CryptoObject which can be used with this IdentityCredential.

If IdentityCredential is not hardware-backed the returned BiometricPrompt.CryptoObject is associated with a java.security.Signature object. If IdentityCredential is hardware-backed, the returned BiometricPrompt.CryptoObject is associated android.security.identity.IdentityCredential object from the Android Framework. Because of this, this method is the preferred way to obtain a BiometricPrompt.CryptoObject rather than to construct it manually.

If the credential has no access control profiles with user-authentication, the value null may be returned.

getEntries

@NonNull abstract fun getEntries(
    @Nullable requestMessage: ByteArray?, 
    @NonNull entriesToRequest: MutableMap<String!, MutableCollection<String!>!>, 
    @Nullable readerSignature: ByteArray?
): ResultData

Retrieve data entries and associated data from this IdentityCredential.

If an access control check fails for one of the requested entries or if the entry doesn't exist, the entry is simply not returned. The application can detect this by using the ResultData#getStatus(String, String) method on each of the requested entries.

It is the responsibility of the calling application to know if authentication is needed and use e.g. androidx.biometric.BiometricPrompt to make the user authenticate using a androidx.biometric.BiometricPrompt.CryptoObject which references this object. If needed, this must be done before calling getEntries(byte[], Map, byte[]).

It is permissible to call this method multiple times using the same instance.

If not null the requestMessage parameter must contain data for the request from the verifier. The content can be defined in the way appropriate for the credential, but there are three requirements that must be met to work with this API:

• The content must be a CBOR-encoded structure.
• The CBOR structure must be a map.
• The map must contain a tstr key "nameSpaces" whose value contains a map, as described in the example below.

If these requirements are not met the InvalidRequestMessageException exception is thrown.

Here's an example of CBOR which conforms to this requirement:

ItemsRequest = {
          ? "docType" : DocType,
          "nameSpaces" : NameSpaces,
          ? "RequestInfo" : {* tstr => any} ; Additional info the reader wants to provide
        }
     
        DocType = tstr
     
        NameSpaces = {
          + NameSpace => DataElements    ; Requested data elements for each NameSpace
        }
     
        NameSpace = tstr
     
        DataElements = {
          + DataElement => IntentToRetain
        }
     
        DataElement = tstr
        IntentToRetain = bool
      

If the setSessionTranscript(byte[]) was called, the X and Y coordinates of the public part of the key-pair previously generated by createEphemeralKeyPair() must appear somewhere in the byte array that was set. Each of these coordinates must appear encoded with the most significant bits first and use the exact amount of bits indicated by the key size of the ephemeral keys. For example, if the ephemeral key is using the P-256 curve then the 32 bytes for the X coordinate encoded with the most significant bits first must appear somewhere in the CBOR and ditto for the 32 bytes for the Y coordinate.

If readerAuth is not null it must be the bytes of a COSE_Sign1 structure as defined in RFC 8152. For the payload nil shall be used and the detached payload is the ReaderAuthenticationBytes CBOR described below.

ReaderAuthentication = [
            "ReaderAuthentication",
            SessionTranscript,
            ItemsRequestBytes
          ]
     
          ItemsRequestBytes = #6.24(bstr .cbor ItemsRequest)
     
          ReaderAuthenticationBytes = #6.24(bstr .cbor ReaderAuthentication)
      

where ItemsRequestBytes are the bytes in the requestMessage parameter.

The public key corresponding to the key used to make the signature, can be found in the x5chain unprotected header element of the COSE_Sign1 structure (as as described in draft-ietf-cose-x509-04). There will be at least one certificate in said element and there may be more (and if so, each certificate must be signed by its successor).

Data elements protected by reader authentication are returned if, and only if, they are mentioned in requestMessage, requestMessage is signed by the top-most certificate in the reader's certificate chain, and the data element is configured with an AccessControlProfile configured with an X.509 certificate which appears in the certificate chain.

Note that only items referenced in entriesToRequest are returned - the requestMessage parameter is used only for enforcing reader authentication.

The reason for having requestMessage and entriesToRequest as separate parameters is that the former represents a request from the remote verifier device (optionally signed) and this allows the application to filter the request to not include data elements which the user has not consented to sharing.

setAllowUsingExhaustedKeys

abstract fun setAllowUsingExhaustedKeys(allowUsingExhaustedKeys: Boolean): Unit

Sets whether to allow using an authentication key which use count has been exceeded if no other key is available. This must be called prior to calling getEntries(byte[], Map, byte[]) or using a android.hardware.biometrics.BiometricPrompt.CryptoObject which references this object. By default this is set to true.

setAvailableAuthenticationKeys

abstract fun setAvailableAuthenticationKeys(
    keyCount: Int, 
    maxUsesPerKey: Int
): Unit

Sets the number of dynamic authentication keys the IdentityCredential will maintain, and the number of times each should be used.

IdentityCredentials will select the least-used dynamic authentication key each time getEntries(byte[], Map, byte[]) is called. IdentityCredentials for which this method has not been called behave as though it had been called wit keyCount 0 and maxUsesPerKey 1.

setReaderEphemeralPublicKey

abstract fun setReaderEphemeralPublicKey(@NonNull readerEphemeralPublicKey: PublicKey): Unit

Set the ephemeral public key provided by the reader. This must be called before encryptMessageToReader or decryptMessageFromReader can be called.

setSessionTranscript

abstract fun setSessionTranscript(@NonNull sessionTranscript: ByteArray): Unit

Set the session transcript. This must be called before encryptMessageToReader or decryptMessageFromReader can be called.

This method can only be called once per IdentityCredential instance.

storeStaticAuthenticationData

abstract fun storeStaticAuthenticationData(
    @NonNull authenticationKey: X509Certificate, 
    @NonNull staticAuthData: ByteArray
): Unit

Store authentication data associated with a dynamic authentication key. This should only be called for an authenticated key returned by getAuthKeysNeedingCertification().