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IdentityCredential

abstract class IdentityCredential
kotlin.Any
   ↳ androidx.security.identity.IdentityCredential

Class used to read data from a previously provisioned credential. Use IdentityCredentialStore#getCredentialByName(String, int) to get a IdentityCredential instance.

Summary

Public methods
abstract KeyPair

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

abstract ByteArray
decryptMessageFromReader(@NonNull messageCiphertext: ByteArray)

Decrypt a message received from the reader.

abstract ByteArray
encryptMessageToReader(@NonNull messagePlaintext: ByteArray)

Encrypt a message for transmission to the reader.

abstract MutableCollection<X509Certificate!>

Gets a collection of dynamic authentication keys that need certification.

abstract IntArray

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

abstract MutableCollection<X509Certificate!>

Gets the X.

abstract BiometricPrompt.CryptoObject?

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

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

Retrieve data entries and associated data from this IdentityCredential.

abstract Unit
setAllowUsingExhaustedKeys(allowUsingExhaustedKeys: Boolean)

Sets whether to allow using an authentication key which use count has been exceeded if no other key is available.

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

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

abstract Unit
setReaderEphemeralPublicKey(@NonNull readerEphemeralPublicKey: PublicKey)

Set the ephemeral public key provided by the reader.

abstract Unit
setSessionTranscript(@NonNull sessionTranscript: ByteArray)

Set the session transcript.

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

Store authentication data associated with a dynamic authentication key.

Public methods

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.

Return
KeyPair ephemeral key pair to use to establish a secure channel with a reader.

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.

Parameters
messageCiphertext ByteArray: encrypted message to decrypt.
Return
ByteArray decrypted message.
Exceptions
MessageDecryptionException if the ciphertext couldn't be decrypted.

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.

Parameters
messagePlaintext ByteArray: unencrypted message to encrypt.
Return
ByteArray encrypted message.

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.

Return
MutableCollection<X509Certificate!> A collection of X.509 certificates for dynamic authentication keys that need issuer certification.

getAuthenticationDataUsageCount

@NonNull abstract fun getAuthenticationDataUsageCount(): IntArray

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

Return
IntArray int array of dynamic authentication key usage counts.

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.

Return
MutableCollection<X509Certificate!> the certificate chain for this credential's CredentialKey.

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.

Return
BiometricPrompt.CryptoObject? A BiometricPrompt.CryptoObject which can be used with BiometricPrompt or null.

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.

Parameters
requestMessage ByteArray?: If not null, must contain CBOR data conforming to the schema mentioned above.
entriesToRequest MutableMap<String!, MutableCollection<String!>!>: The entries to request, organized as a map of namespace names with each value being a collection of data elements in the given namespace.
readerSignature ByteArray?: A COSE_Sign1 structure as described above or null if reader authentication is not being used.
Return
ResultData A ResultData object containing entry data organized by namespace and a cryptographically authenticated representation of the same data.
Exceptions
NoAuthenticationKeyAvailableException is thrown if authentication keys were never provisioned, none are available, or the available ones are all exhausted and setAllowUsingExhaustedKeys(boolean) was called with false.
InvalidReaderSignatureException if the reader signature is invalid, or it doesn't contain a certificate chain, or if the signature failed to validate.
InvalidRequestMessageException if the requestMessage is malformed.
EphemeralPublicKeyNotFoundException if the ephemeral public key was not found in the session transcript.

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.

Parameters
allowUsingExhaustedKeys Boolean: whether to allow using an authentication key which use count has been exceeded if no other key is available.

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.

Parameters
keyCount Int: The number of active, certified dynamic authentication keys the IdentityCredential will try to keep available. This value must be non-negative.
maxUsesPerKey Int: The maximum number of times each of the keys will be used before it's eligible for replacement. This value must be greater than zero.

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.

Parameters
readerEphemeralPublicKey PublicKey: The ephemeral public key provided by the reader to establish a secure session.
Exceptions
InvalidKeyException if the given key is invalid.

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.

Parameters
sessionTranscript ByteArray: the session transcript.

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().

Parameters
authenticationKey X509Certificate: The dynamic authentication key for which certification and associated static authentication data is being provided.
staticAuthData ByteArray: Static authentication data provided by the issuer that validates the authenticity and integrity of the credential data fields.
Exceptions
UnknownAuthenticationKeyException If the given authentication key is not recognized.