I converted an int to a byte array using ByteBuffer's putInt() method. How do I do the opposite? So convert those bytes to an int?
Furthermore, I converted a string to an array of bytes using the String's getBytes() method. How do I convert it the other way round? The bytesArray.getString() does not return a readable string. I get things like BF#DDAD
You can use the ByteBuffer.getInt method, specifying the offset at which the integer occurs, to convert a series of bytes into an integer. Alternatively, if you happen to know the byte ordering, you can use bitwise operators to explicitly reconstruct the 32-bit integer from its 8-bit octets.
To convert an array of bytes into a String, you can use the String(byte[]) constructor to construct a new String out of the byte array. For example:
byte[] bytes = /* ... get array of bytes ... */
String fromBytes = new String(bytes);
Related
I have a function for hashing passwords, that returns a byte[] with entries using the full range of the byte datatype from -128 to 127. I have tried to convert the byte[] to a String using new String(byte_array, StandardCharsets.UTF_8);. This does return a String - however it can not properly encode negative numbers - hence it encodes them to a "�" character. When comparing two of those characters using: new String(new byte[]{-1}, StandardCharsets.UTF_8).equals(new String(new byte[]{-2}, StandardCharsets.UTF_8)) it turns out the String representation for all negative numbers is equal as the expression above returns true. While this doesn't fully ruin my hashing functionality as the hash of the same expression will still always yield the same result, this is obviously not what I want as it increases the chance of two different inputs yielding the same output drastically.
Is there some easy fix for this or any alternative idea how to convert the byte[] to a String? For context I want to use the String to later write it to a file to store it in a file and later read it again to compare it to other hashes.
Edit: After a bit of trying around with the tips from the comments my solution is to convert the byte[] to a char[] and add 128 to every value. The char array can then easily be converted to a String or be written to a file directly (byteHash is the byte[]):
char[] charHash = new char[byteHash.length];
for(int i = 0; i < byteHash.length; i++){
charHash[i] = (char) (byteHash[i]+128);
}
return new String(charHash);
I do not really like the solution but it works.
The appropriate solution to this is to use an encoding like hexadecimal (https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/HexFormat.html) or Base64 (https://docs.oracle.com/javase/8/docs/api/java/util/Base64.html) to convert an arbitrary byte sequence to a string reversibly.
I have an enum
public enum Test {
VALUE, NAME;
}
I convert it into a byte array
byte[] array = Test.VALUE.toString().getBytes(Charsets.UTF_8)
how can i convert that back into an enum?
Test.valueOf(array.toString()) does not work.
The reason why array.toString didn't work is that toString returns a description of the array, not the string constructed using the bytes in the array with UTF-8 encoding. toString just returns something like [B#60e53b93 which means practically nothing to humans.
To convert a byte array to a string, use the string's constructor, the one that takes a byte array and a Charset. Here's the whole code:
// converting to byte array
Test t = Test.VALUE;
byte[] bytes = t.toString().getBytes(StandardCharsets.UTF_8);
// converting back to Test
String str = new String(bytes, StandardCharsets.UTF_8);
Test newT = Test.valueOf(str);
If you think about it logically, toString can't possibly give you what you expect. This is because to convert a byte array to a string, you need to specify an encoding! You obvious did not pass a Charset object when you call toString, so how on earth is the computer going to know what charset you want?
You have to convert the array back to a proper String first using it constructor. array.toString() does not do what you think and will only return gibberish.
byte[] array = Test.VALUE.toString().getBytes(Charsets.UTF_8);
String valueString = new String(array, Charsets.UTF_8);
Test value = Test.valueOf(valueString);
Here below is how I generate a SecureRandom:
byte[] arr = SecureRandom.getInstance("SHA1PRNG").generateSeed(32);
then, I convert it to a string like this:
String str = new String(arr)
and finally, I try to convert the string back to my original byte array:
byte[] arr2 = str.getBytes()
The problem is that the last statement does not return my original byte array... Am I missing something?
then, I convert it to a string like this:
Don't do that!
You have two problems here:
this constructor will use the default encoding;
even if you used UTF-8 as an encoding, some byte sequences just cannot be encoded to chars!
You should not use String to hold binary data; or use a string-based encoding, such as Base64.
For more information, see CharsetDecoder and CodingErrorAction.
Is it possible to convert a byte array to a string but where the length of the string is exactly the same length as the number of bytes in the array? If I use the following:
byte[] data; // Fill it with data
data.toString();
The length of the string is different than the length of the array. I believe that this is because Java and/or Android takes some kind of default encoding into account. The values in the array can be negative as well. Theoretically it should be possible to convert any byte to some character. I guess I need to figure out how to specify an encoding that generates a fixed single byte width for each character.
EDIT:
I tried the following but it didn't work:
byte[] textArray; // Fill this with some text.
String textString = new String(textArray, "ASCII");
textArray = textString.getBytes("ASCII"); // textArray ends up with different data.
You can use the String constructor String(byte[] data) to create a string from the byte array. If you want to specify the charset as well, you can use String(byte[] data, Charset charset) constructor.
Try your code sample with US-ASCII or ISO-8859-1 in place of ASCII. ASCII is not a built-in Character encoding for Java or Android, but one of those two are. They are guaranteed single-byte encodings, with a caveat that characters not in the character set will be silently truncated.
This should work fine!
public static byte[] stringToByteArray(String pStringValue){
int length= pStringValue.length();
byte[] bytes = new byte[length];
for(int index=0; index<length; index++){
char ch= pStringValue.charAt(index);
bytes[index]= (byte)ch;
}
return bytes;
}
since JDK 1.6:
You can also use:
stringValue.getBytes() which will return you a byte array.
In case of passing a NULL string, you need to handle that by either throwing the nullPointerException or handling it inside the method itself.
I try to compare 2 byte arrays.
Byte array 1 is an array with the last 3 bytes of a sha1 hash:
private static byte[] sha1SsidGetBytes(byte[] sha1)
{
return new byte[] {sha1[17], sha1[18], sha1[19]};
}
Byte array 2 is an array that I fill with 3 bytes coming from an hexadecimal string:
private static byte[] ssidGetBytes(String ssid)
{
BigInteger ssidBigInt = new BigInteger(ssid, 16);
return ssidBigInt.toByteArray();
}
How is it possible that this comparison:
if (Arrays.equals(ssidBytes, sha1SsidGetBytes(snSha1)))
{
}
works most of the times but sometimes not. Byte Order?
e.g. for "6451E6" (hex string) it works fine, for "ABED74" it does not...
The problem is pretty obvious if you try this:
BigInteger b1 = new BigInteger("6451E6", 16);
BigInteger b2 = new BigInteger("ABED74", 16);
System.out.println(b1.toByteArray().length);
System.out.println(b2.toByteArray().length);
Specifically, ABED74 creates a BigInteger whose byte array is 4 bytes long--so of course it's not going to be equal to any three byte array.
The straightforward fix is to change the return statement in ssidGetBytes from
return ssidBigInt.toByteArray();
to
byte[] ba = ssidBigInt.toByteArray();
return new byte[] { ba[ba.length - 3], ba[ba.length - 2], ba[ba.length - 1] };
Your approach of parsing a hex string via BigInteger is flawed, basically. For example, new BigInteger("ABED74").toByteArray() returns an array of 4 bytes, not three. While you could hack around this, you're fundamentally not trying to do anything involving BigInteger values... you're just trying to parse hex.
I suggest you use the Apache Codec library to do the parsing:
byte[] array = (byte[]) new Hex().decode(text);
(The API for Apache Codec leaves something to be desired, but it does work.)
From the javadoc's (emphasis mine):
http://download.oracle.com/javase/1.5.0/docs/api/java/math/BigInteger.html#toByteArray%28%29
Returns a byte array containing the
two's-complement representation of
this BigInteger. The byte array will
be in big-endian byte-order: the most
significant byte is in the zeroth
element. The array will contain the
minimum number of bytes required to
represent this BigInteger, including
at least one sign bit, which is
(ceil((this.bitLength() + 1)/8)).
(This representation is compatible
with the (byte[]) constructor.)
There is a lot of computations going on inside the ByteInteger(String,radix) constructor that you are using, which does not guarantee the constructed BigInteger will produce a byte array (via its toByteArray() method) comparable to the result of a String's getBytes() encoding.
The output of toByteArray() is intended to be used (mostly) as input to the (byte[]) constructor of BigInteger. It makes no guarantee for uses other than those.
Look at it like this: the output of toByteArray() is the byte representation of the BigInteger object and everything in it including internal attributes like magnitude. Those attributes do not exist in the input String, but are computed during construction of the BitInteger object.
That will be incompatible to the byte representation of the input String which only carries the initial numeric value with which to create a BigInteger.