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/*
* Copyright (C) 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.libraries.entitlement.eapaka;
import android.text.TextUtils;
import android.util.Base64;
import android.util.Log;
import com.android.libraries.entitlement.ServiceEntitlementException;
/**
* Provide format to handle request/response SIM Authentication with GSM/3G security context.
*
* <p>Reference ETSI TS 131 102, Section 7.1.2.1 GSM/3G security context.
*/
class EapAkaSecurityContext {
private static final String TAG = "ServiceEntitlement";
private static final byte RESPONSE_TAG_SUCCESS = (byte) 0xDB;
private boolean valid;
/* Authentication result from SIM */
private byte[] res;
/* Cipher Key */
private byte[] ck;
/* Integrity Key */
private byte[] ik;
private EapAkaSecurityContext() {
}
/** Provide {@link EapAkaSecurityContext} from response data. */
public static EapAkaSecurityContext from(String response)
throws ServiceEntitlementException {
EapAkaSecurityContext securityContext = new EapAkaSecurityContext();
securityContext.parseResponseData(response);
if (!securityContext.isValid()) {
throw new ServiceEntitlementException("Invalid SIM EAP-AKA authentication response!");
}
return securityContext;
}
/**
* Parses SIM EAP-AKA Authentication responsed data and returns valid {@link
* EapAkaSecurityContext}
* for successful data; otherwise, returns invalid.
*/
void parseResponseData(String response) {
if (TextUtils.isEmpty(response)) {
Log.d(TAG, "parseResponseData but input empty data!");
return;
}
try {
byte[] data = Base64.decode(response, Base64.DEFAULT);
Log.d(TAG, "decoded data length=" + data.length);
if (data.length <= 2) {
return;
}
int index = 0;
// check tag
if (data[index] != RESPONSE_TAG_SUCCESS) {
Log.d(TAG, "Not successful data, tag=" + data[index]);
return;
}
// Parse RES
index++; // move to RES length byte
res = parseTag(index, data);
if (res == null) {
Log.d(TAG, "Invalid data! can't parse RES!");
return;
}
// Parse CK
index += res.length + 1; // move to CK length byte
ck = parseTag(index, data);
if (ck == null) {
Log.d(TAG, "Invalid data! can't parse CK!");
return;
}
// Parse IK
index += ck.length + 1; // move to IK length byte
ik = parseTag(index, data);
if (ik == null) {
Log.d(TAG, "Invalid data! can't parse IK!");
return;
}
valid = true;
} catch (IllegalArgumentException illegalArgumentException) {
Log.e(TAG, "Invalid base-64 content");
}
}
private byte[] parseTag(int index, byte[] src) {
// index at the length byte
if (index >= src.length) {
Log.d(TAG, "No length byte!");
return null;
}
int length = src[index] & 0xff;
if (index + length >= src.length) {
Log.d(TAG, "Invalid data length!");
return null;
}
index++; // move to first byte of tag value
byte[] dest = new byte[length];
System.arraycopy(src, index, dest, 0, length);
return dest;
}
/** Returns {@code valid}. */
boolean isValid() {
return valid;
}
/** Returns {@code res}. */
public byte[] getRes() {
return res;
}
/** Returns {@code ck}. */
public byte[] getCk() {
return ck;
}
/** Returns {@code ik}. */
public byte[] getIk() {
return ik;
}
}
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