XOR operation with two strings in java

Question

How to do bitwise XOR operation to two strings in java

User · Answer

This is the code I m using   private static byte   xor final byte   input  final byte   secret        final byte   output   new byte input length       if  secret length    0            throw new IllegalArgumentException  empty security key              int spos   0      for  int pos   0  pos  lt  input length    pos            output pos     byte   input pos    secret spos              spos          if  spos  gt   secret length                spos   0                      return output

User · Answer

the abs function is when the Strings are not the same length so the legth of the result will be the same as the min lenght of the two String a and b   public String xor String a  String b       StringBuilder sb   new StringBuilder        for int k 0  k  lt  a length    k           sb append  a charAt k    b charAt k    Math abs a length   - b length                 return sb toString

User · Answer

You want something like this   import sun misc BASE64Decoder  import sun misc BASE64Encoder  import java io IOException   public class StringXORer        public String encode String s  String key            return base64Encode xorWithKey s getBytes    key getBytes                 public String decode String s  String key            return new String xorWithKey base64Decode s   key getBytes                 private byte   xorWithKey byte   a  byte   key            byte   out   new byte a length           for  int i   0  i  lt  a length  i                  out i     byte   a i    key i key length                      return out             private byte   base64Decode String s            try               BASE64Decoder d   new BASE64Decoder                return d decodeBuffer s             catch  IOException e   throw new RuntimeException e               private String base64Encode byte   bytes            BASE64Encoder enc   new BASE64Encoder            return enc encode bytes  replaceAll    s                   The base64 encoding is done because xor ing the bytes of a string may not give valid bytes back for a string

User · Answer

This solution is compatible with Android  I ve tested and used it myself   Thanks to  user467257 whose solution I adapted this from   import android util Base64   public class StringXORer    public String encode String s  String key        return new String Base64 encode xorWithKey s getBytes    key getBytes     Base64 DEFAULT       public String decode String s  String key        return new String xorWithKey base64Decode s   key getBytes         private byte   xorWithKey byte   a  byte   key        byte   out   new byte a length       for  int i   0  i  lt  a length  i              out i     byte   a i    key i key length              return out     private byte   base64Decode String s        return Base64 decode s Base64 DEFAULT      private String base64Encode byte   bytes        return new String Base64 encode bytes Base64 DEFAULT

User · Answer

Pay attention   A Java char corresponds to a UTF-16 code unit  and in some cases two consecutive chars  a so-called surrogate pair  are needed for one real Unicode character  codepoint    XORing two valid UTF-16 sequences  i e  Java Strings char by char  or byte by byte after encoding to UTF-16  does not necessarily give you another valid UTF-16 string - you may have unpaired surrogates as a result   It would still be a perfectly usable Java String  just the codepoint-concerning methods could get confused  and the ones that convert to other encodings for output and similar    The same is valid if you first convert your Strings to UTF-8 and then XOR these bytes - here you quite probably will end up with a byte sequence which is not valid UTF-8  if your Strings were not already both pure ASCII strings   Even if you try to do it right and iterate over your two Strings by codepoint and try to XOR the codepoints  you can end up with codepoints outside the valid range  for example  U FFFFF  plane 15  XOR U 10000  plane 16    U 1FFFFF  which would the last character of plane 31   way above the range of existing codepoints  And you could also end up this way with codepoints reserved for surrogates    not valid ones    If your strings only contain chars  lt  128  256  512  1024  2048  4096  8192  16384  or 32768  then the  char-wise  XORed strings will be in the same range  and thus certainly not contain any surrogates  In the first two cases you could also encode your String as ASCII or Latin-1  respectively  and have the same XOR-result for the bytes   You still can end up with control chars  which may be a problem for you      What I m finally saying here  don t expect the result of encrypting Strings to be a valid string again - instead  simply store and transmit it as a byte    or a stream of bytes    And yes  convert to UTF-8 before encrypting  and from UTF-8 after decrypting

User · Answer

Note  this only works for low characters i e  below 0x8000  This works for all ASCII characters   I would do an XOR each charAt   to create a new String  Like  String s  key   StringBuilder sb   new StringBuilder    for int i   0  i  lt  s length    i        sb append  char  s charAt i    key charAt i   key length       String result   sb toString        In response to  user467257 s comment     If your input output is utf-8 and you xor  a  and       you are left with an invalid utf-8 string consisting of one character  decimal 135  a continuation character      It is the char values which are being xor ed  but the byte values and this produces a character whichc an be UTF-8 encoded   public static void main String    args  throws UnsupportedEncodingException       char ch1    a       char ch2             char ch3    char   ch1   ch2       System out println  int  ch3     UTF-8 encoded is     Arrays toString String valueOf ch3  getBytes  UTF-8          prints  135 UTF-8 encoded is  -62  -121

User · Answer

Assuming     the strings are of equal length  why not convert the strings to byte arrays and then XOR the bytes  The resultant byte arrays may be of different lengths too depending on your encoding  e g  UTF8 will expand to different byte lengths for different characters     You should be careful to specify the character encoding to ensure consistent reliable string byte conversion

[java] XOR operation with two strings in java

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