TLS-PSK is a set of TLS/SSL cipher suites which rely on a symmetric pre-shared key (PSK) to * secure the TLS/SSL connection and mutually authenticate its peers. These cipher suites may be * a more natural fit compared to conventional public key based cipher suites in some scenarios * where communication between peers is bootstrapped via a separate step (for example, a pairing * step) and requires both peers to authenticate each other. In such scenarios a symmetric key (PSK) * can be exchanged during the bootstrapping step, removing the need to generate and exchange public * key pairs and X.509 certificates.
* *When a TLS-PSK cipher suite is used, both peers have to use the same key for the TLS/SSL * handshake to succeed. Thus, both peers are implicitly authenticated by a successful handshake. * This removes the need to use a {@code TrustManager} in conjunction with this {@code KeyManager}. *
* *A peer may have multiple keys to choose from. To help choose the right key, during the * handshake the server can provide a PSK identity hint to the client, and the client can * provide a PSK identity to the server. The contents of these two pieces of information * are specific to application-level protocols.
* *NOTE: Both the PSK identity hint and the PSK identity are transmitted in cleartext. * Moreover, these data are received and processed prior to peer having been authenticated. Thus, * they must not contain or leak key material or other sensitive information, and should be * treated (e.g., parsed) with caution, as untrusted data.
* *The high-level flow leading to peers choosing a key during TLS/SSL handshake is as follows: *
In the flow above, either peer can signal that they do not have a suitable key, in which case * the the handshake will be aborted immediately. This may enable a network attacker who does not * know the key to learn which PSK identity hints or PSK identities are supported. If this is a * concern then a randomly generated key should be used in the scenario where no key is available. * This will lead to the handshake aborting later, due to key mismatch -- same as in the scenario * where a key is available -- making it appear to the attacker that all PSK identity hints and PSK * identities are supported.
* *The maximum supported sizes are as follows: *
{@code
* PskKeyManager pskKeyManager = ...;
*
* SSLContext sslContext = SSLContext.getInstance("TLS");
* sslContext.init(
* new KeyManager[] {pskKeyManager},
* new TrustManager[0], // No TrustManagers needed for TLS-PSK
* null // Use the default source of entropy
* );
*
* SSLSocket sslSocket = (SSLSocket) sslContext.getSocketFactory().createSocket(...);
* }
*/
public abstract class PskKeyManager implements PSKKeyManager {
// IMPLEMENTATION DETAILS: This class exists only because the default implemenetation of the
// TLS/SSL JSSE provider (currently Conscrypt) cannot depend on Android framework classes.
// As a result, this framework class simply extends the PSKKeyManager interface from Conscrypt
// without adding any new methods or fields. Moreover, for technical reasons (Conscrypt classes
// are "hidden") this class replaces the Javadoc of Conscrypt's PSKKeyManager.
/**
* Maximum supported length (in bytes) for PSK identity hint (in modified UTF-8 representation).
*/
public static final int MAX_IDENTITY_HINT_LENGTH_BYTES =
PSKKeyManager.MAX_IDENTITY_HINT_LENGTH_BYTES;
/** Maximum supported length (in bytes) for PSK identity (in modified UTF-8 representation). */
public static final int MAX_IDENTITY_LENGTH_BYTES = PSKKeyManager.MAX_IDENTITY_LENGTH_BYTES;
/** Maximum supported length (in bytes) for PSK. */
public static final int MAX_KEY_LENGTH_BYTES = PSKKeyManager.MAX_KEY_LENGTH_BYTES;
/**
* Gets the PSK identity hint to report to the client to help agree on the PSK for the provided
* socket.
*
* * The default implementation returns {@code null}. * * @return PSK identity hint to be provided to the client or {@code null} to provide no hint. */ @Override public String chooseServerKeyIdentityHint(Socket socket) { return null; } /** * Gets the PSK identity hint to report to the client to help agree on the PSK for the provided * engine. * *
* The default implementation returns {@code null}. * * @return PSK identity hint to be provided to the client or {@code null} to provide no hint. */ @Override public String chooseServerKeyIdentityHint(SSLEngine engine) { return null; } /** * Gets the PSK identity to report to the server to help agree on the PSK for the provided * socket. * *
* The default implementation returns an empty string. * * @param identityHint identity hint provided by the server or {@code null} if none provided. * * @return PSK identity to provide to the server. {@code null} is permitted but will be * converted into an empty string. */ @Override public String chooseClientKeyIdentity(String identityHint, Socket socket) { return ""; } /** * Gets the PSK identity to report to the server to help agree on the PSK for the provided * engine. * *
* The default implementation returns an empty string. * * @param identityHint identity hint provided by the server or {@code null} if none provided. * * @return PSK identity to provide to the server. {@code null} is permitted but will be * converted into an empty string. */ @Override public String chooseClientKeyIdentity(String identityHint, SSLEngine engine) { return ""; } /** * Gets the PSK to use for the provided socket. * *
* The default implementation returns {@code null}. * * @param identityHint identity hint provided by the server to help select the key or * {@code null} if none provided. * @param identity identity provided by the client to help select the key. * * @return key or {@code null} to signal to peer that no suitable key is available and to abort * the handshake. */ @Override public SecretKey getKey(String identityHint, String identity, Socket socket) { return null; } /** * Gets the PSK to use for the provided engine. * *
* The default implementation returns {@code null}. * * @param identityHint identity hint provided by the server to help select the key or * {@code null} if none provided. * @param identity identity provided by the client to help select the key. * * @return key or {@code null} to signal to peer that no suitable key is available and to abort * the handshake. */ @Override public SecretKey getKey(String identityHint, String identity, SSLEngine engine) { return null; } }