KeyGenParameterSpec
class KeyGenParameterSpec : AlgorithmParameterSpec
kotlin.Any | |
↳ | android.security.keystore.KeyGenParameterSpec |
AlgorithmParameterSpec
for initializing a KeyPairGenerator
or a KeyGenerator
of the Android Keystore system. The spec determines authorized uses of the key, such as whether user authentication is required for using the key, what operations are authorized (e.g., signing, but not decryption), with what parameters (e.g., only with a particular padding scheme or digest), and the key's validity start and end dates. Key use authorizations expressed in the spec apply only to secret keys and private keys -- public keys can be used for any supported operations.
To generate an asymmetric key pair or a symmetric key, create an instance of this class using the Builder
, initialize a KeyPairGenerator
or a KeyGenerator
of the desired key type (e.g., EC
or AES
-- see KeyProperties
.KEY_ALGORITHM
constants) from the AndroidKeyStore
provider with the KeyGenParameterSpec
instance, and then generate a key or key pair using KeyGenerator#generateKey()
or KeyPairGenerator#generateKeyPair()
.
The generated key pair or key will be returned by the generator and also stored in the Android Keystore under the alias specified in this spec. To obtain the secret or private key from the Android Keystore use KeyStore.getKey(String, null)
or KeyStore.getEntry(String, null)
. To obtain the public key from the Android Keystore use java.security.KeyStore#getCertificate(String)
and then Certificate#getPublicKey()
.
To help obtain algorithm-specific public parameters of key pairs stored in the Android Keystore, generated private keys implement java.security.interfaces.ECKey
or java.security.interfaces.RSAKey
interfaces whereas public keys implement java.security.interfaces.ECPublicKey
or java.security.interfaces.RSAPublicKey
interfaces.
For asymmetric key pairs, a X.509 certificate will be also generated and stored in the Android Keystore. This is because the java.security.KeyStore
abstraction does not support storing key pairs without a certificate. The subject, serial number, and validity dates of the certificate can be customized in this spec. The certificate may be replaced at a later time by a certificate signed by a Certificate Authority (CA).
NOTE: If attestation is not requested using Builder#setAttestationChallenge(byte[])
, generated certificate may be self-signed. If a private key is not authorized to sign the certificate, then the certificate will be created with an invalid signature which will not verify. Such a certificate is still useful because it provides access to the public key. To generate a valid signature for the certificate the key needs to be authorized for all of the following:
KeyProperties#PURPOSE_SIGN
,- operation without requiring the user to be authenticated (see
Builder#setUserAuthenticationRequired(boolean)
), - signing/origination at this moment in time (see
Builder#setKeyValidityStart(Date)
andBuilder#setKeyValidityForOriginationEnd(Date)
), - suitable digest,
- (RSA keys only) padding scheme
KeyProperties#SIGNATURE_PADDING_RSA_PKCS1
.
NOTE: The key material of the generated symmetric and private keys is not accessible. The key material of the public keys is accessible.
Instances of this class are immutable.
Known issues
A known bug in Android 6.0 (API Level 23) causes user authentication-related authorizations to be enforced even for public keys. To work around this issue extract the public key material to use outside of Android Keystore. For example:<code>PublicKey unrestrictedPublicKey = KeyFactory.getInstance(publicKey.getAlgorithm()).generatePublic( new X509EncodedKeySpec(publicKey.getEncoded())); </code>
Example: NIST P-256 EC key pair for signing/verification using ECDSA
This example illustrates how to generate a NIST P-256 (aka secp256r1 aka prime256v1) EC key pair in the Android KeyStore system under aliaskey1
where the private key is authorized to be used only for signing using SHA-256, SHA-384, or SHA-512 digest and only if the user has been authenticated within the last five minutes. The use of the public key is unrestricted (See Known Issues).
<code>KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance( KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore"); keyPairGenerator.initialize( new KeyGenParameterSpec.Builder( "key1", KeyProperties.PURPOSE_SIGN) .setAlgorithmParameterSpec(new ECGenParameterSpec("secp256r1")) .setDigests(KeyProperties.DIGEST_SHA256, KeyProperties.DIGEST_SHA384, KeyProperties.DIGEST_SHA512) // Only permit the private key to be used if the user authenticated // within the last five minutes. .setUserAuthenticationRequired(true) .setUserAuthenticationValidityDurationSeconds(5 * 60) .build()); KeyPair keyPair = keyPairGenerator.generateKeyPair(); Signature signature = Signature.getInstance("SHA256withECDSA"); signature.initSign(keyPair.getPrivate()); ... // The key pair can also be obtained from the Android Keystore any time as follows: KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore"); keyStore.load(null); PrivateKey privateKey = (PrivateKey) keyStore.getKey("key1", null); PublicKey publicKey = keyStore.getCertificate("key1").getPublicKey(); </code>
Example: RSA key pair for signing/verification using RSA-PSS
This example illustrates how to generate an RSA key pair in the Android KeyStore system under aliaskey1
authorized to be used only for signing using the RSA-PSS signature padding scheme with SHA-256 or SHA-512 digests. The use of the public key is unrestricted.
<code>KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance( KeyProperties.KEY_ALGORITHM_RSA, "AndroidKeyStore"); keyPairGenerator.initialize( new KeyGenParameterSpec.Builder( "key1", KeyProperties.PURPOSE_SIGN) .setDigests(KeyProperties.DIGEST_SHA256, KeyProperties.DIGEST_SHA512) .setSignaturePaddings(KeyProperties.SIGNATURE_PADDING_RSA_PSS) .build()); KeyPair keyPair = keyPairGenerator.generateKeyPair(); Signature signature = Signature.getInstance("SHA256withRSA/PSS"); signature.initSign(keyPair.getPrivate()); ... // The key pair can also be obtained from the Android Keystore any time as follows: KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore"); keyStore.load(null); PrivateKey privateKey = (PrivateKey) keyStore.getKey("key1", null); PublicKey publicKey = keyStore.getCertificate("key1").getPublicKey(); </code>
Example: RSA key pair for encryption/decryption using RSA OAEP
This example illustrates how to generate an RSA key pair in the Android KeyStore system under aliaskey1
where the private key is authorized to be used only for decryption using RSA OAEP encryption padding scheme with SHA-256 or SHA-512 digests. The use of the public key is unrestricted.
<code>KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance( KeyProperties.KEY_ALGORITHM_RSA, "AndroidKeyStore"); keyPairGenerator.initialize( new KeyGenParameterSpec.Builder( "key1", KeyProperties.PURPOSE_DECRYPT) .setDigests(KeyProperties.DIGEST_SHA256, KeyProperties.DIGEST_SHA512) .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_OAEP) .build()); KeyPair keyPair = keyPairGenerator.generateKeyPair(); Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding"); cipher.init(Cipher.DECRYPT_MODE, keyPair.getPrivate()); ... // The key pair can also be obtained from the Android Keystore any time as follows: KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore"); keyStore.load(null); PrivateKey privateKey = (PrivateKey) keyStore.getKey("key1", null); PublicKey publicKey = keyStore.getCertificate("key1").getPublicKey(); </code>
Example: AES key for encryption/decryption in GCM mode
The following example illustrates how to generate an AES key in the Android KeyStore system under aliaskey2
authorized to be used only for encryption/decryption in GCM mode with no padding.
<code>KeyGenerator keyGenerator = KeyGenerator.getInstance( KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore"); keyGenerator.init( new KeyGenParameterSpec.Builder("key2", KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT) .setBlockModes(KeyProperties.BLOCK_MODE_GCM) .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE) .build()); SecretKey key = keyGenerator.generateKey(); Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding"); cipher.init(Cipher.ENCRYPT_MODE, key); ... // The key can also be obtained from the Android Keystore any time as follows: KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore"); keyStore.load(null); key = (SecretKey) keyStore.getKey("key2", null); </code>
Example: HMAC key for generating a MAC using SHA-256
This example illustrates how to generate an HMAC key in the Android KeyStore system under aliaskey2
authorized to be used only for generating an HMAC using SHA-256.
<code>KeyGenerator keyGenerator = KeyGenerator.getInstance( KeyProperties.KEY_ALGORITHM_HMAC_SHA256, "AndroidKeyStore"); keyGenerator.init( new KeyGenParameterSpec.Builder("key2", KeyProperties.PURPOSE_SIGN).build()); SecretKey key = keyGenerator.generateKey(); Mac mac = Mac.getInstance("HmacSHA256"); mac.init(key); ... // The key can also be obtained from the Android Keystore any time as follows: KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore"); keyStore.load(null); key = (SecretKey) keyStore.getKey("key2", null); </code>
Example: EC key for ECDH key agreement
This example illustrates how to generate an elliptic curve key pair, used to establish a shared secret with another party using ECDH key agreement.<code>KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance( KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore"); keyPairGenerator.initialize( new KeyGenParameterSpec.Builder( "eckeypair", KeyProperties.PURPOSE_AGREE_KEY) .setAlgorithmParameterSpec(new ECGenParameterSpec("secp256r1")) .build()); KeyPair myKeyPair = keyPairGenerator.generateKeyPair(); // Exchange public keys with server. A new ephemeral key MUST be used for every message. PublicKey serverEphemeralPublicKey; // Ephemeral key received from server. // Create a shared secret based on our private key and the other party's public key. KeyAgreement keyAgreement = KeyAgreement.getInstance("ECDH", "AndroidKeyStore"); keyAgreement.init(myKeyPair.getPrivate()); keyAgreement.doPhase(serverEphemeralPublicKey, true); byte[] sharedSecret = keyAgreement.generateSecret(); // sharedSecret cannot safely be used as a key yet. We must run it through a key derivation // function with some other data: "salt" and "info". Salt is an optional random value, // omitted in this example. It's good practice to include both public keys and any other // key negotiation data in info. Here we use the public keys and a label that indicates // messages encrypted with this key are coming from the server. byte[] salt = {}; ByteArrayOutputStream info = new ByteArrayOutputStream(); info.write("ECDH secp256r1 AES-256-GCM-SIV\0".getBytes(StandardCharsets.UTF_8)); info.write(myKeyPair.getPublic().getEncoded()); info.write(serverEphemeralPublicKey.getEncoded()); // This example uses the Tink library and the HKDF key derivation function. AesGcmSiv key = new AesGcmSiv(Hkdf.computeHkdf( "HMACSHA256", sharedSecret, salt, info.toByteArray(), 32)); byte[] associatedData = {}; return key.decrypt(ciphertext, associatedData); </code>
Summary
Nested classes | |
---|---|
Builder of |
Public methods | |
---|---|
AlgorithmParameterSpec? |
Returns the key algorithm-specific |
String? |
Returns the alias of the attestation key that will be used to sign the attestation certificate of the generated key. |
ByteArray! |
Returns the attestation challenge value that will be placed in attestation certificate for this key pair. |
Array<String!> |
Gets the set of block modes (e.g., |
Date |
Returns the end date to be used on the X. |
Date |
Returns the start date to be used on the X. |
BigInteger |
Returns the serial number to be used on the X. |
X500Principal |
Returns the subject distinguished name to be used on the X. |
Array<String!> |
Returns the set of digest algorithms (e.g., |
Array<String!> |
Returns the set of padding schemes (e.g., |
Int |
Returns the requested key size. |
Date? |
Returns the time instant after which the key is no longer valid for decryption and verification or |
Date? |
Returns the time instant after which the key is no longer valid for encryption and signing or |
Date? |
Returns the time instant before which the key is not yet valid or |
String |
Returns the alias that will be used in the |
Int |
Returns the maximum number of times the limited use key is allowed to be used or |
MutableSet<String!> |
Returns the set of digests that can be used by the MGF1 mask generation function (e.g., |
Int |
Returns the set of purposes (e.g., encrypt, decrypt, sign) for which the key can be used. |
Array<String!> |
Gets the set of padding schemes (e.g., |
Int |
Gets the modes of authentication that can authorize use of this key. |
Int |
Gets the duration of time (seconds) for which this key is authorized to be used after the user is successfully authenticated. |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Boolean |
Returns |
Public methods
getAlgorithmParameterSpec
fun getAlgorithmParameterSpec(): AlgorithmParameterSpec?
Returns the key algorithm-specific AlgorithmParameterSpec
that will be used for creation of the key or null
if algorithm-specific defaults should be used.
getAttestKeyAlias
fun getAttestKeyAlias(): String?
Returns the alias of the attestation key that will be used to sign the attestation certificate of the generated key. Note that an attestation certificate will only be generated if an attestation challenge is set.
Return | |
---|---|
String? |
This value may be null . |
getAttestationChallenge
fun getAttestationChallenge(): ByteArray!
Returns the attestation challenge value that will be placed in attestation certificate for this key pair.
If this method returns non-null
, the public key certificate for this key pair will contain an extension that describes the details of the key's configuration and authorizations, including the content of the attestation challenge value. If the key is in secure hardware, and if the secure hardware supports attestation, the certificate will be signed by a chain of certificates rooted at a trustworthy CA key. Otherwise the chain will be rooted at an untrusted certificate.
If this method returns null
, and the spec is used to generate an asymmetric (RSA or EC) key pair, the public key will have a self-signed certificate if it has purpose android.security.keystore.KeyProperties#PURPOSE_SIGN
. If does not have purpose KeyProperties#PURPOSE_SIGN
, it will have a fake certificate.
Symmetric keys, such as AES and HMAC keys, do not have public key certificates. If a KeyGenParameterSpec with getAttestationChallenge returning non-null is used to generate a symmetric (AES or HMAC) key, javax.crypto.KeyGenerator#generateKey()
will throw java.security.InvalidAlgorithmParameterException
.
getBlockModes
fun getBlockModes(): Array<String!>
Gets the set of block modes (e.g., GCM
, CBC
) with which the key can be used when encrypting/decrypting. Attempts to use the key with any other block modes will be rejected.
See KeyProperties
.BLOCK_MODE
constants.
getCertificateNotAfter
fun getCertificateNotAfter(): Date
Returns the end date to be used on the X.509 certificate that will be put in the java.security.KeyStore
.
Return | |
---|---|
Date |
This value cannot be null . |
getCertificateNotBefore
fun getCertificateNotBefore(): Date
Returns the start date to be used on the X.509 certificate that will be put in the java.security.KeyStore
.
Return | |
---|---|
Date |
This value cannot be null . |
getCertificateSerialNumber
fun getCertificateSerialNumber(): BigInteger
Returns the serial number to be used on the X.509 certificate that will be put in the java.security.KeyStore
.
Return | |
---|---|
BigInteger |
This value cannot be null . |
getCertificateSubject
fun getCertificateSubject(): X500Principal
Returns the subject distinguished name to be used on the X.509 certificate that will be put in the java.security.KeyStore
.
Return | |
---|---|
X500Principal |
This value cannot be null . |
getDigests
fun getDigests(): Array<String!>
Returns the set of digest algorithms (e.g., SHA-256
, SHA-384
with which the key can be used.
See KeyProperties
.DIGEST
constants.
Exceptions | |
---|---|
java.lang.IllegalStateException |
if this set has not been specified. |
See Also
getEncryptionPaddings
fun getEncryptionPaddings(): Array<String!>
Returns the set of padding schemes (e.g., PKCS7Padding
, OEAPPadding
, PKCS1Padding
, NoPadding
) with which the key can be used when encrypting/decrypting. Attempts to use the key with any other padding scheme will be rejected.
See KeyProperties
.ENCRYPTION_PADDING
constants.
getKeySize
fun getKeySize(): Int
Returns the requested key size. If -1
, the size should be looked up from getAlgorithmParameterSpec()
, if provided, otherwise an algorithm-specific default size should be used.
getKeyValidityForConsumptionEnd
fun getKeyValidityForConsumptionEnd(): Date?
Returns the time instant after which the key is no longer valid for decryption and verification or null
if not restricted.
getKeyValidityForOriginationEnd
fun getKeyValidityForOriginationEnd(): Date?
Returns the time instant after which the key is no longer valid for encryption and signing or null
if not restricted.
getKeyValidityStart
fun getKeyValidityStart(): Date?
Returns the time instant before which the key is not yet valid or null
if not restricted.
getKeystoreAlias
fun getKeystoreAlias(): String
Returns the alias that will be used in the java.security.KeyStore
in conjunction with the AndroidKeyStore
.
Return | |
---|---|
String |
This value cannot be null . |
getMaxUsageCount
fun getMaxUsageCount(): Int
Returns the maximum number of times the limited use key is allowed to be used or KeyProperties#UNRESTRICTED_USAGE_COUNT
if there’s no restriction on the number of times the key can be used.
getMgf1Digests
fun getMgf1Digests(): MutableSet<String!>
Returns the set of digests that can be used by the MGF1 mask generation function (e.g., SHA-256
, SHA-384
) with the key. Useful with the RSA-OAEP
scheme. If not explicitly specified during key generation, the default SHA-1
digest is used and may be specified when using the key.
See KeyProperties
.DIGEST
constants.
Exceptions | |
---|---|
java.lang.IllegalStateException |
if this set has not been specified. |
See Also
getPurposes
fun getPurposes(): Int
Returns the set of purposes (e.g., encrypt, decrypt, sign) for which the key can be used. Attempts to use the key for any other purpose will be rejected.
See KeyProperties
.PURPOSE
flags.
getSignaturePaddings
fun getSignaturePaddings(): Array<String!>
Gets the set of padding schemes (e.g., PSS
, PKCS#1
) with which the key can be used when signing/verifying. Attempts to use the key with any other padding scheme will be rejected.
See KeyProperties
.SIGNATURE_PADDING
constants.
Return | |
---|---|
Array<String!> |
This value cannot be null . Value is android.security.keystore.KeyProperties#SIGNATURE_PADDING_RSA_PKCS1 , or android.security.keystore.KeyProperties#SIGNATURE_PADDING_RSA_PSS |
getUserAuthenticationType
fun getUserAuthenticationType(): Int
Gets the modes of authentication that can authorize use of this key. This has effect only if user authentication is required (see isUserAuthenticationRequired()
).
This authorization applies only to secret key and private key operations. Public key operations are not restricted.
Return | |
---|---|
Int |
integer representing the bitwse OR of all acceptable authentication types for the key. Value is either 0 or a combination of android.security.keystore.KeyProperties#AUTH_BIOMETRIC_STRONG , and android.security.keystore.KeyProperties#AUTH_DEVICE_CREDENTIAL |
getUserAuthenticationValidityDurationSeconds
fun getUserAuthenticationValidityDurationSeconds(): Int
Gets the duration of time (seconds) for which this key is authorized to be used after the user is successfully authenticated. This has effect only if user authentication is required (see isUserAuthenticationRequired()
).
This authorization applies only to secret key and private key operations. Public key operations are not restricted.
Return | |
---|---|
Int |
duration in seconds or -1 if authentication is required for every use of the key. |
isDevicePropertiesAttestationIncluded
fun isDevicePropertiesAttestationIncluded(): Boolean
Returns true
if attestation for the base device properties (Build#BRAND
, Build#DEVICE
, Build#MANUFACTURER
, Build#MODEL
, Build#PRODUCT
) was requested to be added in the attestation certificate for the generated key. javax.crypto.KeyGenerator#generateKey()
will throw java.security.ProviderException
if device properties attestation fails or is not supported.
isDigestsSpecified
fun isDigestsSpecified(): Boolean
Returns true
if the set of digest algorithms with which the key can be used has been specified.
Return | |
---|---|
Boolean |
This value cannot be null . |
See Also
isInvalidatedByBiometricEnrollment
fun isInvalidatedByBiometricEnrollment(): Boolean
Returns true
if the key is irreversibly invalidated when a new biometric is enrolled or all enrolled biometrics are removed. This has effect only for keys that require biometric user authentication for every use.
isMgf1DigestsSpecified
fun isMgf1DigestsSpecified(): Boolean
Returns true
if the set of digests for the MGF1 mask generation function, with which the key can be used, has been specified. Useful with the RSA-OAEP
scheme.
Return | |
---|---|
Boolean |
This value cannot be null . |
See Also
isRandomizedEncryptionRequired
fun isRandomizedEncryptionRequired(): Boolean
Returns true
if encryption using this key must be sufficiently randomized to produce different ciphertexts for the same plaintext every time. The formal cryptographic property being required is indistinguishability under chosen-plaintext attack (IND-CPA
). This property is important because it mitigates several classes of weaknesses due to which ciphertext may leak information about plaintext. For example, if a given plaintext always produces the same ciphertext, an attacker may see the repeated ciphertexts and be able to deduce something about the plaintext.
isStrongBoxBacked
fun isStrongBoxBacked(): Boolean
Returns true
if the key is protected by a Strongbox security chip.
isUnlockedDeviceRequired
fun isUnlockedDeviceRequired(): Boolean
Returns true
if the key is authorized to be used only while the device is unlocked.
isUserAuthenticationRequired
fun isUserAuthenticationRequired(): Boolean
Returns true
if the key is authorized to be used only if the user has been authenticated.
This authorization applies only to secret key and private key operations. Public key operations are not restricted.
isUserAuthenticationValidWhileOnBody
fun isUserAuthenticationValidWhileOnBody(): Boolean
Returns true
if the key will remain authorized only until the device is removed from the user's body, up to the validity duration. This option has no effect on keys that don't have an authentication validity duration, and has no effect if the device lacks an on-body sensor.
Authorization applies only to secret key and private key operations. Public key operations are not restricted.
isUserConfirmationRequired
fun isUserConfirmationRequired(): Boolean
Returns true
if the key is authorized to be used only for messages confirmed by the user. Confirmation is separate from user authentication (see Builder#setUserAuthenticationRequired(boolean)
). Keys can be created that require confirmation but not user authentication, or user authentication but not confirmation, or both. Confirmation verifies that some user with physical possession of the device has approved a displayed message. User authentication verifies that the correct user is present and has authenticated.
This authorization applies only to secret key and private key operations. Public key operations are not restricted.
isUserPresenceRequired
fun isUserPresenceRequired(): Boolean
Returns true
if the key is authorized to be used only if a test of user presence has been performed between the Signature.initSign()
and Signature.sign()
calls. It requires that the KeyStore implementation have a direct way to validate the user presence for example a KeyStore hardware backed strongbox can use a button press that is observable in hardware. A test for user presence is tangential to authentication. The test can be part of an authentication step as long as this step can be validated by the hardware protecting the key and cannot be spoofed. For example, a physical button press can be used as a test of user presence if the other pins connected to the button are not able to simulate a button press. There must be no way for the primary processor to fake a button press, or that button must not be used as a test of user presence.