安卓base64与其他语言base64算法还原出来差异问题？？？

今天逆向某app时，发现了最后一步base64编码后后几位不一致。

之前有遇到空格及换行等问题，eg :

在在线工具生成对比后，确实后几位有出入。
回看了代码base64就是调用的标准算法，且也没更换码表。

# 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
# 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

众所周知，base64是以6位进行便宜，而正常是8个bit位，这样就会缺两位进行==补位。

祥细解说及码表更换base64：https://codeooo.blog.csdn.net/article/details/119810268

经过分析代码：

而我们常规的：

    public static final String m54667a(String str, String str2) {String str3 = "(this as java.lang.String).getBytes(charset)";m73751b(str, "content");m73751b(str2, "password");byte[] bArr = null;try {byte[] bytes = str2.getBytes(StandardCharsets.UTF_8);m73745a((Object) bytes, str3);SecretKeySpec secretKeySpec = new SecretKeySpec(bytes, "AES");Cipher instance = Cipher.getInstance("AES/CBC/PKCS5Padding");Charset forName = StandardCharsets.UTF_8;m73745a((Object) forName, "Charset.forName(charsetName)");byte[] bytes2 = str.getBytes(forName);m73745a((Object) bytes2, str3);byte[] bytes3 = str2.getBytes(StandardCharsets.UTF_8);m73745a((Object) bytes3, str3);instance.init(1, secretKeySpec, new IvParameterSpec(bytes3));String encodeToString = Base64.getEncoder().encodeToString(instance.doFinal(bytes2));m73745a((Object) encodeToString, "Base64.encodeToString(en…ptResult, Base64.NO_WRAP)");return encodeToString;} catch (Exception e) {e.printStackTrace();return "";}}

故而我们可以使用：

引入一个三方jar包：
com.akdeniz.googleplaycrawler.misc.Base64

import com.akdeniz.googleplaycrawler.misc.Base64; //导入依赖的package包/类public class encryptString {/****/public static String main(String str2Encrypt) throws Exception {byte[] keyByteArray = Base64.decode(GOOGLE_PUBLIC_KEY, Base64.DEFAULT);byte[] header = new byte[5];byte[] digest = MessageDigest.getInstance("SHA-1").digest(keyByteArray);header[0] = 0;System.arraycopy(digest, 0, header, 1, 4);PublicKey publicKey = createKey(keyByteArray);Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWITHSHA1ANDMGF1PADDING");byte[] bytes2Encrypt = str2Encrypt.getBytes("UTF-8");int len = ((bytes2Encrypt.length - 1) / 86) + 1;byte[] cryptedBytes = new byte[len * 133];for (int j = 0; j < len; j++) {cipher.init(1, publicKey);byte[] arrayOfByte4 = cipher.doFinal(bytes2Encrypt, j * 86, (bytes2Encrypt.length - j * 86));System.arraycopy(header, 0, cryptedBytes, j * 133, header.length);System.arraycopy(arrayOfByte4, 0, cryptedBytes, j * 133 + header.length, arrayOfByte4.length);}return Base64.encodeToString(cryptedBytes, 10);}
}

另一种解决方案：

直接将安卓的base64代码copy进来，就一个文件

/** Copyright (C) 2010 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 android.util;import java.io.UnsupportedEncodingException;/*** Utilities for encoding and decoding the Base64 representation of* binary data.  See RFCs <a* href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a* href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.*/
public class Base64 {/*** Default values for encoder/decoder flags.*/public static final int DEFAULT = 0;/*** Encoder flag bit to omit the padding '=' characters at the end* of the output (if any).*/public static final int NO_PADDING = 1;/*** Encoder flag bit to omit all line terminators (i.e., the output* will be on one long line).*/public static final int NO_WRAP = 2;/*** Encoder flag bit to indicate lines should be terminated with a* CRLF pair instead of just an LF.  Has no effect if {@code* NO_WRAP} is specified as well.*/public static final int CRLF = 4;/*** Encoder/decoder flag bit to indicate using the "URL and* filename safe" variant of Base64 (see RFC 3548 section 4) where* {@code -} and {@code _} are used in place of {@code +} and* {@code /}.*/public static final int URL_SAFE = 8;/*** Flag to pass to {@link Base64OutputStream} to indicate that it* should not close the output stream it is wrapping when it* itself is closed.*/public static final int NO_CLOSE = 16;//  --------------------------------------------------------//  shared code//  --------------------------------------------------------/* package */ static abstract class Coder {public byte[] output;public int op;/*** Encode/decode another block of input data.  this.output is* provided by the caller, and must be big enough to hold all* the coded data.  On exit, this.opwill be set to the length* of the coded data.** @param finish true if this is the final call to process for*        this object.  Will finalize the coder state and*        include any final bytes in the output.** @return true if the input so far is good; false if some*         error has been detected in the input stream..*/public abstract boolean process(byte[] input, int offset, int len, boolean finish);/*** @return the maximum number of bytes a call to process()* could produce for the given number of input bytes.  This may* be an overestimate.*/public abstract int maxOutputSize(int len);}//  --------------------------------------------------------//  decoding//  --------------------------------------------------------/*** Decode the Base64-encoded data in input and return the data in* a new byte array.** <p>The padding '=' characters at the end are considered optional, but* if any are present, there must be the correct number of them.** @param str    the input String to decode, which is converted to*               bytes using the default charset* @param flags  controls certain features of the decoded output.*               Pass {@code DEFAULT} to decode standard Base64.** @throws IllegalArgumentException if the input contains* incorrect padding*/public static byte[] decode(String str, int flags) {return decode(str.getBytes(), flags);}/*** Decode the Base64-encoded data in input and return the data in* a new byte array.** <p>The padding '=' characters at the end are considered optional, but* if any are present, there must be the correct number of them.** @param input the input array to decode* @param flags  controls certain features of the decoded output.*               Pass {@code DEFAULT} to decode standard Base64.** @throws IllegalArgumentException if the input contains* incorrect padding*/public static byte[] decode(byte[] input, int flags) {return decode(input, 0, input.length, flags);}/*** Decode the Base64-encoded data in input and return the data in* a new byte array.** <p>The padding '=' characters at the end are considered optional, but* if any are present, there must be the correct number of them.** @param input  the data to decode* @param offset the position within the input array at which to start* @param len    the number of bytes of input to decode* @param flags  controls certain features of the decoded output.*               Pass {@code DEFAULT} to decode standard Base64.** @throws IllegalArgumentException if the input contains* incorrect padding*/public static byte[] decode(byte[] input, int offset, int len, int flags) {// Allocate space for the most data the input could represent.// (It could contain less if it contains whitespace, etc.)Decoder decoder = new Decoder(flags, new byte[len*3/4]);if (!decoder.process(input, offset, len, true)) {throw new IllegalArgumentException("bad base-64");}// Maybe we got lucky and allocated exactly enough output space.if (decoder.op == decoder.output.length) {return decoder.output;}// Need to shorten the array, so allocate a new one of the// right size and copy.byte[] temp = new byte[decoder.op];System.arraycopy(decoder.output, 0, temp, 0, decoder.op);return temp;}/* package */ static class Decoder extends Coder {/*** Lookup table for turning bytes into their position in the* Base64 alphabet.*/private static final int DECODE[] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,-1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,};/*** Decode lookup table for the "web safe" variant (RFC 3548* sec. 4) where - and _ replace + and /.*/private static final int DECODE_WEBSAFE[] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1,52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,-1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63,-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,};/** Non-data values in the DECODE arrays. */private static final int SKIP = -1;private static final int EQUALS = -2;/*** States 0-3 are reading through the next input tuple.* State 4 is having read one '=' and expecting exactly* one more.* State 5 is expecting no more data or padding characters* in the input.* State 6 is the error state; an error has been detected* in the input and no future input can "fix" it.*/private int state;   // state number (0 to 6)private int value;final private int[] alphabet;public Decoder(int flags, byte[] output) {this.output = output;alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;state = 0;value = 0;}/*** @return an overestimate for the number of bytes {@code* len} bytes could decode to.*/public int maxOutputSize(int len) {return len * 3/4 + 10;}/*** Decode another block of input data.** @return true if the state machine is still healthy.  false if*         bad base-64 data has been detected in the input stream.*/public boolean process(byte[] input, int offset, int len, boolean finish) {if (this.state == 6) return false;int p = offset;len += offset;// Using local variables makes the decoder about 12%// faster than if we manipulate the member variables in// the loop.  (Even alphabet makes a measurable// difference, which is somewhat surprising to me since// the member variable is final.)int state = this.state;int value = this.value;int op = 0;final byte[] output = this.output;final int[] alphabet = this.alphabet;while (p < len) {// Try the fast path:  we're starting a new tuple and the// next four bytes of the input stream are all data// bytes.  This corresponds to going through states// 0-1-2-3-0.  We expect to use this method for most of// the data.//// If any of the next four bytes of input are non-data// (whitespace, etc.), value will end up negative.  (All// the non-data values in decode are small negative// numbers, so shifting any of them up and or'ing them// together will result in a value with its top bit set.)//// You can remove this whole block and the output should// be the same, just slower.if (state == 0) {while (p+4 <= len &&(value = ((alphabet[input[p] & 0xff] << 18) |(alphabet[input[p+1] & 0xff] << 12) |(alphabet[input[p+2] & 0xff] << 6) |(alphabet[input[p+3] & 0xff]))) >= 0) {output[op+2] = (byte) value;output[op+1] = (byte) (value >> 8);output[op] = (byte) (value >> 16);op += 3;p += 4;}if (p >= len) break;}// The fast path isn't available -- either we've read a// partial tuple, or the next four input bytes aren't all// data, or whatever.  Fall back to the slower state// machine implementation.int d = alphabet[input[p++] & 0xff];switch (state) {case 0:if (d >= 0) {value = d;++state;} else if (d != SKIP) {this.state = 6;return false;}break;case 1:if (d >= 0) {value = (value << 6) | d;++state;} else if (d != SKIP) {this.state = 6;return false;}break;case 2:if (d >= 0) {value = (value << 6) | d;++state;} else if (d == EQUALS) {// Emit the last (partial) output tuple;// expect exactly one more padding character.output[op++] = (byte) (value >> 4);state = 4;} else if (d != SKIP) {this.state = 6;return false;}break;case 3:if (d >= 0) {// Emit the output triple and return to state 0.value = (value << 6) | d;output[op+2] = (byte) value;output[op+1] = (byte) (value >> 8);output[op] = (byte) (value >> 16);op += 3;state = 0;} else if (d == EQUALS) {// Emit the last (partial) output tuple;// expect no further data or padding characters.output[op+1] = (byte) (value >> 2);output[op] = (byte) (value >> 10);op += 2;state = 5;} else if (d != SKIP) {this.state = 6;return false;}break;case 4:if (d == EQUALS) {++state;} else if (d != SKIP) {this.state = 6;return false;}break;case 5:if (d != SKIP) {this.state = 6;return false;}break;}}if (!finish) {// We're out of input, but a future call could provide// more.this.state = state;this.value = value;this.op = op;return true;}// Done reading input.  Now figure out where we are left in// the state machine and finish up.switch (state) {case 0:// Output length is a multiple of three.  Fine.break;case 1:// Read one extra input byte, which isn't enough to// make another output byte.  Illegal.this.state = 6;return false;case 2:// Read two extra input bytes, enough to emit 1 more// output byte.  Fine.output[op++] = (byte) (value >> 4);break;case 3:// Read three extra input bytes, enough to emit 2 more// output bytes.  Fine.output[op++] = (byte) (value >> 10);output[op++] = (byte) (value >> 2);break;case 4:// Read one padding '=' when we expected 2.  Illegal.this.state = 6;return false;case 5:// Read all the padding '='s we expected and no more.// Fine.break;}this.state = state;this.op = op;return true;}}//  --------------------------------------------------------//  encoding//  --------------------------------------------------------/*** Base64-encode the given data and return a newly allocated* String with the result.** @param input  the data to encode* @param flags  controls certain features of the encoded output.*               Passing {@code DEFAULT} results in output that*               adheres to RFC 2045.*/public static String encodeToString(byte[] input, int flags) {try {return new String(encode(input, flags), "US-ASCII");} catch (UnsupportedEncodingException e) {// US-ASCII is guaranteed to be available.throw new AssertionError(e);}}/*** Base64-encode the given data and return a newly allocated* String with the result.** @param input  the data to encode* @param offset the position within the input array at which to*               start* @param len    the number of bytes of input to encode* @param flags  controls certain features of the encoded output.*               Passing {@code DEFAULT} results in output that*               adheres to RFC 2045.*/public static String encodeToString(byte[] input, int offset, int len, int flags) {try {return new String(encode(input, offset, len, flags), "US-ASCII");} catch (UnsupportedEncodingException e) {// US-ASCII is guaranteed to be available.throw new AssertionError(e);}}/*** Base64-encode the given data and return a newly allocated* byte[] with the result.** @param input  the data to encode* @param flags  controls certain features of the encoded output.*               Passing {@code DEFAULT} results in output that*               adheres to RFC 2045.*/public static byte[] encode(byte[] input, int flags) {return encode(input, 0, input.length, flags);}/*** Base64-encode the given data and return a newly allocated* byte[] with the result.** @param input  the data to encode* @param offset the position within the input array at which to*               start* @param len    the number of bytes of input to encode* @param flags  controls certain features of the encoded output.*               Passing {@code DEFAULT} results in output that*               adheres to RFC 2045.*/public static byte[] encode(byte[] input, int offset, int len, int flags) {Encoder encoder = new Encoder(flags, null);// Compute the exact length of the array we will produce.int output_len = len / 3 * 4;// Account for the tail of the data and the padding bytes, if any.if (encoder.do_padding) {if (len % 3 > 0) {output_len += 4;}} else {switch (len % 3) {case 0: break;case 1: output_len += 2; break;case 2: output_len += 3; break;}}// Account for the newlines, if any.if (encoder.do_newline && len > 0) {output_len += (((len-1) / (3 * Encoder.LINE_GROUPS)) + 1) *(encoder.do_cr ? 2 : 1);}encoder.output = new byte[output_len];encoder.process(input, offset, len, true);assert encoder.op == output_len;return encoder.output;}/* package */ static class Encoder extends Coder {/*** Emit a new line every this many output tuples.  Corresponds to* a 76-character line length (the maximum allowable according to* <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).*/public static final int LINE_GROUPS = 19;/*** Lookup table for turning Base64 alphabet positions (6 bits)* into output bytes.*/private static final byte ENCODE[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P','Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f','g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v','w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',};/*** Lookup table for turning Base64 alphabet positions (6 bits)* into output bytes.*/private static final byte ENCODE_WEBSAFE[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P','Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f','g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v','w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_',};final private byte[] tail;/* package */ int tailLen;private int count;final public boolean do_padding;final public boolean do_newline;final public boolean do_cr;final private byte[] alphabet;public Encoder(int flags, byte[] output) {this.output = output;do_padding = (flags & NO_PADDING) == 0;do_newline = (flags & NO_WRAP) == 0;do_cr = (flags & CRLF) != 0;alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;tail = new byte[2];tailLen = 0;count = do_newline ? LINE_GROUPS : -1;}/*** @return an overestimate for the number of bytes {@code* len} bytes could encode to.*/public int maxOutputSize(int len) {return len * 8/5 + 10;}public boolean process(byte[] input, int offset, int len, boolean finish) {// Using local variables makes the encoder about 9% faster.final byte[] alphabet = this.alphabet;final byte[] output = this.output;int op = 0;int count = this.count;int p = offset;len += offset;int v = -1;// First we need to concatenate the tail of the previous call// with any input bytes available now and see if we can empty// the tail.switch (tailLen) {case 0:// There was no tail.break;case 1:if (p+2 <= len) {// A 1-byte tail with at least 2 bytes of// input available now.v = ((tail[0] & 0xff) << 16) |((input[p++] & 0xff) << 8) |(input[p++] & 0xff);tailLen = 0;};break;case 2:if (p+1 <= len) {// A 2-byte tail with at least 1 byte of input.v = ((tail[0] & 0xff) << 16) |((tail[1] & 0xff) << 8) |(input[p++] & 0xff);tailLen = 0;}break;}if (v != -1) {output[op++] = alphabet[(v >> 18) & 0x3f];output[op++] = alphabet[(v >> 12) & 0x3f];output[op++] = alphabet[(v >> 6) & 0x3f];output[op++] = alphabet[v & 0x3f];if (--count == 0) {if (do_cr) output[op++] = '\r';output[op++] = '\n';count = LINE_GROUPS;}}// At this point either there is no tail, or there are fewer// than 3 bytes of input available.// The main loop, turning 3 input bytes into 4 output bytes on// each iteration.while (p+3 <= len) {v = ((input[p] & 0xff) << 16) |((input[p+1] & 0xff) << 8) |(input[p+2] & 0xff);output[op] = alphabet[(v >> 18) & 0x3f];output[op+1] = alphabet[(v >> 12) & 0x3f];output[op+2] = alphabet[(v >> 6) & 0x3f];output[op+3] = alphabet[v & 0x3f];p += 3;op += 4;if (--count == 0) {if (do_cr) output[op++] = '\r';output[op++] = '\n';count = LINE_GROUPS;}}if (finish) {// Finish up the tail of the input.  Note that we need to// consume any bytes in tail before any bytes// remaining in input; there should be at most two bytes// total.if (p-tailLen == len-1) {int t = 0;v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;tailLen -= t;output[op++] = alphabet[(v >> 6) & 0x3f];output[op++] = alphabet[v & 0x3f];if (do_padding) {output[op++] = '=';output[op++] = '=';}if (do_newline) {if (do_cr) output[op++] = '\r';output[op++] = '\n';}} else if (p-tailLen == len-2) {int t = 0;v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) |(((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);tailLen -= t;output[op++] = alphabet[(v >> 12) & 0x3f];output[op++] = alphabet[(v >> 6) & 0x3f];output[op++] = alphabet[v & 0x3f];if (do_padding) {output[op++] = '=';}if (do_newline) {if (do_cr) output[op++] = '\r';output[op++] = '\n';}} else if (do_newline && op > 0 && count != LINE_GROUPS) {if (do_cr) output[op++] = '\r';output[op++] = '\n';}assert tailLen == 0;assert p == len;} else {// Save the leftovers in tail to be consumed on the next// call to encodeInternal.if (p == len-1) {tail[tailLen++] = input[p];} else if (p == len-2) {tail[tailLen++] = input[p];tail[tailLen++] = input[p+1];}}this.op = op;this.count = count;return true;}}private Base64() { }   // don't instantiate
}

完美解决~

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安卓base64与其他语言base64算法还原出来差异问题？？？

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