1 /* 2 * Copyright 2014 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package org.conscrypt; 18 19 import java.net.Socket; 20 import javax.crypto.SecretKey; 21 import javax.net.ssl.KeyManager; 22 import javax.net.ssl.SSLEngine; 23 24 /** 25 * Provider of key material for pre-shared key (PSK) key exchange used in TLS-PSK cipher suites. 26 * 27 * <h3>Overview of TLS-PSK</h3> 28 * 29 * <p>TLS-PSK is a set of TLS/SSL cipher suites which rely on a symmetric pre-shared key (PSK) to 30 * secure the TLS/SSL connection and mutually authenticate its peers. These cipher suites may be 31 * a more natural fit compared to conventional public key based cipher suites in some scenarios 32 * where communication between peers is bootstrapped via a separate step (for example, a pairing 33 * step) and requires both peers to authenticate each other. In such scenarios a symmetric key (PSK) 34 * can be exchanged during the bootstrapping step, removing the need to generate and exchange public 35 * key pairs and X.509 certificates.</p> 36 * 37 * <p>When a TLS-PSK cipher suite is used, both peers have to use the same key for the TLS/SSL 38 * handshake to succeed. Thus, both peers are implicitly authenticated by a successful handshake. 39 * This removes the need to use a {@code TrustManager} in conjunction with this {@code KeyManager}. 40 * </p> 41 * 42 * <h3>Supporting multiple keys</h3> 43 * 44 * <p>A peer may have multiple keys to choose from. To help choose the right key, during the 45 * handshake the server can provide a <em>PSK identity hint</em> to the client, and the client can 46 * provide a <em>PSK identity</em> to the server. The contents of these two pieces of information 47 * are specific to application-level protocols.</p> 48 * 49 * <p><em>NOTE: Both the PSK identity hint and the PSK identity are transmitted in cleartext. 50 * Moreover, these data are received and processed prior to peer having been authenticated. Thus, 51 * they must not contain or leak key material or other sensitive information, and should be 52 * treated (e.g., parsed) with caution, as untrusted data.</em></p> 53 * 54 * <p>The high-level flow leading to peers choosing a key during TLS/SSL handshake is as follows: 55 * <ol> 56 * <li>Server receives a handshake request from client. 57 * <li>Server replies, optionally providing a PSK identity hint to client.</li> 58 * <li>Client chooses the key.</li> 59 * <li>Client provides a PSK identity of the chosen key to server.</li> 60 * <li>Server chooses the key.</li> 61 * </ol></p> 62 * 63 * <p>In the flow above, either peer can signal that they do not have a suitable key, in which case 64 * the the handshake will be aborted immediately. This may enable a network attacker who does not 65 * know the key to learn which PSK identity hints or PSK identities are supported. If this is a 66 * concern then a randomly generated key should be used in the scenario where no key is available. 67 * This will lead to the handshake aborting later, due to key mismatch -- same as in the scenario 68 * where a key is available -- making it appear to the attacker that all PSK identity hints and PSK 69 * identities are supported.</p> 70 * 71 * <h3>Maximum sizes</h3> 72 * 73 * <p>The maximum supported sizes are as follows: 74 * <ul> 75 * <li>256 bytes for keys (see {@link #MAX_KEY_LENGTH_BYTES}),</li> 76 * <li>128 bytes for PSK identity and PSK identity hint (in modified UTF-8 representation) (see 77 * {@link #MAX_IDENTITY_LENGTH_BYTES} and {@link #MAX_IDENTITY_HINT_LENGTH_BYTES}).</li> 78 * </ul></p> 79 * 80 * <h3>Example</h3> 81 * The following example illustrates how to create an {@code SSLContext} which enables the use of 82 * TLS-PSK in {@code SSLSocket}, {@code SSLServerSocket} and {@code SSLEngine} instances obtained 83 * from it. 84 * <pre> {@code 85 * PSKKeyManager myPskKeyManager = ...; 86 * 87 * SSLContext sslContext = SSLContext.getInstance("TLS"); 88 * sslContext.init( 89 * new KeyManager[] {myPskKeyManager}, 90 * new TrustManager[0], // No TrustManagers needed for TLS-PSK 91 * null // Use the default source of entropy 92 * ); 93 * 94 * SSLSocket sslSocket = (SSLSocket) sslContext.getSocketFactory().createSocket(...); 95 * }</pre> 96 */ 97 public interface PSKKeyManager extends KeyManager { 98 99 /** 100 * Maximum supported length (in bytes) for PSK identity hint (in modified UTF-8 representation). 101 */ 102 int MAX_IDENTITY_HINT_LENGTH_BYTES = 128; 103 104 /** Maximum supported length (in bytes) for PSK identity (in modified UTF-8 representation). */ 105 int MAX_IDENTITY_LENGTH_BYTES = 128; 106 107 /** Maximum supported length (in bytes) for PSK key. */ 108 int MAX_KEY_LENGTH_BYTES = 256; 109 110 /** 111 * Gets the PSK identity hint to report to the client to help agree on the PSK for the provided 112 * socket. 113 * 114 * @return PSK identity hint to be provided to the client or {@code null} to provide no hint. 115 */ 116 String chooseServerKeyIdentityHint(Socket socket); 117 118 /** 119 * Gets the PSK identity hint to report to the client to help agree on the PSK for the provided 120 * engine. 121 * 122 * @return PSK identity hint to be provided to the client or {@code null} to provide no hint. 123 */ 124 String chooseServerKeyIdentityHint(SSLEngine engine); 125 126 /** 127 * Gets the PSK identity to report to the server to help agree on the PSK for the provided 128 * socket. 129 * 130 * @param identityHint identity hint provided by the server or {@code null} if none provided. 131 * 132 * @return PSK identity to provide to the server. {@code null} is permitted but will be 133 * converted into an empty string. 134 */ 135 String chooseClientKeyIdentity(String identityHint, Socket socket); 136 137 /** 138 * Gets the PSK identity to report to the server to help agree on the PSK for the provided 139 * engine. 140 * 141 * @param identityHint identity hint provided by the server or {@code null} if none provided. 142 * 143 * @return PSK identity to provide to the server. {@code null} is permitted but will be 144 * converted into an empty string. 145 */ 146 String chooseClientKeyIdentity(String identityHint, SSLEngine engine); 147 148 /** 149 * Gets the PSK to use for the provided socket. 150 * 151 * @param identityHint identity hint provided by the server to help select the key or 152 * {@code null} if none provided. 153 * @param identity identity provided by the client to help select the key. 154 * 155 * @return key or {@code null} to signal to peer that no suitable key is available and to abort 156 * the handshake. 157 */ 158 SecretKey getKey(String identityHint, String identity, Socket socket); 159 160 /** 161 * Gets the PSK to use for the provided engine. 162 * 163 * @param identityHint identity hint provided by the server to help select the key or 164 * {@code null} if none provided. 165 * @param identity identity provided by the client to help select the key. 166 * 167 * @return key or {@code null} to signal to peer that no suitable key is available and to abort 168 * the handshake. 169 */ 170 SecretKey getKey(String identityHint, String identity, SSLEngine engine); 171 }
