I an working on ECIES and need to load peer public key.
Load EC Public key
I an using ECDH and need to load peer public key.
When I try to load public key from PEM file , seems no issue
Issue here:
EVP_PKEY * get_peer_key()
{
// base64 certificate data of alice_pub_key.pem
char *buffer= "MFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEjWrT7F97QrSqGrlIgPK8dphNBicNO6gDLfOIMjhF2MiLuuzd7L7BP+bLCuNtKKe/2dOkgPqgXv4BFWqgp6PZXQ=="`
// calculate buffer length
int l = strlen(buffer)
//create bio from buffer
BIO *in = BIO_new_mem_buf(buffer,l)
//gnerate ec key
EC_KEY *eckey = PEM_read_bio_EC_PUBKEY(in,NULL,NULL,NULL)` // ==> FAIL
//need to convert to EVP format
EVP_PKEY *peerKey = EVP_PKEY_new()
//assign ec key evp
if(EVP_PKEY_assign_EC_KEY(peerKey,eckey) != 1 )
printf("\n error hapened");
return peerKey;
}
Works fine:
EVP_PKEY * get_peer_key()
{
//Load PEM format file
char * infile = "alice_pub_key.pem";
//create bio
BIO *in = BIO_new(BIO_s_file());
//read bio file
BIO_read_filename(in , infile);
//create eckey
EC_KEY *eckey = PEM_read_bio_EC_PUBKEY(in,NULL,NULL,NULL); // ==> success
// create peer key
EVP_PKEY *peerKey = EVP_PKEY_new();
//assign public key
if(EVP_PKEY_assign_EC_KEY(peerKey,eckey) != 1 )
printf("\n error hapened");
return peerKey;
}
Can some one suggest whats going wrong while reading base64 data of pem file
There are two ways of solving this:
Creating a PEM using a header and footer line and line breaks (at the 64th character;
Base 64 decoding the text and then handling it by parsing the resulting ASN.1 / DER binary;
I'd prefer the latter, as I abhor adding lines and such, it is error prone at best, and string manipulations should be avoided where possible.
Note that this assumes that the base 64 contains a SubjectPublicKeyInfo structure which I've shown you earlier. Otherwise you may have to find out how to parse a X9.62 structure or just a point.
I am trying to create a software lighting desk by using Qt and Arduino with a DMX Shield. I've been able to establish communication between these two and can send commands over to Arduino Mega (at the moment the communication goes only one way). I am periodically (every 200 ms) sending values of 11 faders to Mega as a String.
eg.: A123 B234 C050 ... J222 M255
The values in the string above are variables based on the position of the sliders and should be used to adjust the values of light intensities saved into each fader on the Mega side. The Letters in each section identify corresponding fader. A = fader1, B = fader2, ... Just for clarity: I can bring up a light/s at a specific intensity -> these intensities are then assigned to a fader and when that fader is moved I want these values to adjust and be sent out to the actual lights/dimmers. The calculations work fine but my Mega would eventually become unresponsive.
I think my problem is parsing the incoming string. I have tried the strtok() method and readStringUntil() to no avail. It is also difficult to monitor the incoming strings in Serial Monitor as this is used for the communication with Qt.
Would be happy for any kind of help. Please ask questions if anything is unclear.
Edit:
This is one of my attempts at solutions
const char delim[2] = " ";
char *token;
if(Serial.available())
{
//incomingMessage = Serial.readString();
incomingMessage = Serial.readStringUntil("\n"); // read the whole string until newline
//Serial.println(incomingMessage);
const char* str = incomingMessage.c_str(); // convert it to a C String terminated by a null character "\0"
//Serial.println(str);
token = strtok(str, delim); // first part is a first section until delimiter occurs "-space- "
//Serial.println(token);
LX_Rated.commandLineResolve(token); // resolve it
while( token != NULL ) { // continue splitting and resolving the incoming message until it reaches the end
token = strtok(NULL, delim);
LX_Rated.commandLineResolve(token);
}
}
Edit2:
I have confirmed that I receive the whole string sent by Qt. When I try to tokenise it using the strtok() function and print out the first token I get back the whole string, the other tokens are empty. I don't see any mistake in my code here. I even tried to slow down the sending of the string from Qt to one per 5 sec. Does anybody have any idea what is going on? I don't see why this standard function doesn't work as expected. Please see the amended code below.
if(Serial.available()) {
incomingMessage = Serial.readStringUntil("\n");
Serial.println("ok");
Serial.flush();
char* nullTerminatedIncomingMessage = incomingMessage.c_str();
const char delimiter = " ";
char* token;
char* token1;
char* token2;
//char* secondToken;
token = strtok(nullTerminatedIncomingMessage, delimiter);
token1 = strtok(NULL, delimiter);
token2 = strtok(NULL, delimiter);
Serial.println(token); // print the first section
//Serial.println(incomingMessage);
Serial.flush();
Serial.println(token1);
Serial.flush();
Serial.println(token2);
Serial.flush();
//while(token != NULL)
// secondToken = strtok(NULL, delimiter);
//Serial.println(secondToken);
//Serial.flush();
incomingMessage = "";
}
Your mistake - at the very least - is in assuming that all the input is available when you expect it. You need to defer processing until an entire line has been assembled. Serial.readStringUntil blocks until an entire line is available, and that's not what you expect. You essentially need to replace Serial.available() with Serial.lineAvailable(), except the latter is not implemented.
This answer contains a complete solution to your issue - including both Qt and Arduino code - and an Arudino emulation layer. It might be a good starting point, especially that you can easily co-debug both Qt and Arduino projects from within one application and using one debugger!
As for difficulty in monitoring communication, you can(in Qt) dump everything you read into console and do the same for everything you write into the serial port. It will show in the console tab of QtCreator
#include <QDebug>
...
qDebug() << "whatever" << endl;
Aso for parsing the data you read from to serial port, take a look at this to see how to easily split the sliders info into individual strings(with QRegExp)
How Can I Split a String According To Delimiters in Qt?
I can't possibly guess why your arduino would be unresponsive without the code.
EDIT:
Is it possible, when you generate the string in Qt, that you separate the tokens by something other than space? Maybe tab("\t") or something? strtok accepts multiple delimiters in the delimiter string, may be something to try.
If that is not the case, there is the unlikely possibility that something's wrong with the strtok(...) function(btw. it modifies the original string, that in itself could be a problem). Also, strtok could return a NULL pointer, you don't seem to handle that case(some wrong input - print a message). You could try this as an alternative to normal strtok:
/**
* #brief custom strtok replacement with the same interface
* It does not modify the original string
* Token length is limited to 63 characters
* #param ptr pointer to the string or NULL
* #param delim delimiting character(only the first character will be used)
*/
const char * my_strtok(const char * ptr, const char * delim) {
// Persistent variables, it will remember pointer to the processed string
static const char * src;
static char buffer[64]; // Token is limited to 63 characters
if(ptr) { // Remember the pointer, if a new one was supplied
src = ptr;
}
if(src == NULL || *src == '\0')// Invalid / empty string / no next token - return NULL
return NULL;
char i = 0;
for(i = 0; i < 63 && *src != delim[0]; i++) {// Copy token until delimiter or end of buffer
buffer[i] = *(src++);
}
if(*src == delim[0]) // Skip over the delimiter to the begining of the next token
++src;
buffer[i] = '\0'; // Any returned string must be terminated
return buffer;
}
#include <cstdlib>
#include <cstring>
#include <cassert>
void test() {
const char * str1 = "123 456 asdf jkl;";
assert(strcmp("123", my_strtok(str1, " ")) == 0);
assert(strcmp("456", my_strtok(NULL, " ")) == 0);
assert(strcmp("asdf", my_strtok(NULL, " ")) == 0);
assert(strcmp("jkl;", my_strtok(NULL, " ")) == 0);
assert(NULL == my_strtok(NULL, " "));
assert(NULL == my_strtok(NULL, " "));
assert(strcmp("123", my_strtok(str1, " ")) == 0);
}
I'm trying to store binary data in a QR code. Apparently QR codes do support storing raw binary data (or ISO-8859-1 / Latin1). Here is what I want to encode (hex):
d1 50 01 00 00 00 f6 5f 05 2d 8f 0b 40 e2 01
I've tried the following encoders:
qr.js
Google Charts
qrcode.js
Decoding with zxing.org produces various incorrect results. The two javascript ones produce this (it's wrong; the first text character should be Ñ.
Whereas Google Charts produces this...
What is going on? Are any of these correct? What's really weird is that if I encode this sequence (with the JS ones at least) then it works fine - I would have thought the issue was non-ASCII characters but Ñ (0xd1) is non-ASCII.
d1 50 01 00 00 00 01 02 03 04 05 06 40 e2 01
Does anyone know what is going on?
Update
It occurred to me to try scanning them with a ZBar-based scanner app I found. It scans both JS versions ok (at least they start with ÑP). The Google Charts one is just wrong. So it seems like the issue is with ZXing (which is surprisingly shit - I wouldn't recommend it to anyone).
Update 2
ZBar can't handle null bytes. :-(
"What is going on? Are any of these correct?"
Except for the google chart (which is just empty), your QR codes are correct.
You can see the binary data from zxing is what you would expect:
4: Byte mode indicator
0f: length of 15 byte
d15001...: your 15 bytes of data
ec11 is just padding
The problem comes from the decoding. Because most decoders will try to interpret it as text. But since it's binary data, you should not try to handle it as text. Even if you think you can convert it from text to binary, as you saw this may cause issues with values which are not valid text.
So the solution is to use a decoder that will output you the binary data, and not text data.
Now about interpreting the QR code binary data as text, you said the first character should be 'Ñ' which is true if interpreted it as "ISO-8859-1",
which according to the QR code standard, is what should be done when there is no ECI mode defined.
But in practice, most smartphone QR code reader will interpret it as UTF-8 in this case (or at least try to auto-detect the encoding).
Even though this is not the standard, this had become common practice:
binary mode with no ECI, UTF-8 encoded text.
Maybe the reason behind it is that no one wants to waste these precious bytes adding an ECI mode specifying UTF-8. And actually, not all decoders support ECI.
There are two issues that you have to overcome to store binary data in QR codes.
ISO-8859-1 does not allow bytes in ranges of 00-1F and 7F-9F. If you
need to encode these bytes anyway, quote or encode them, i.e. use
quoted-printable or Base-64 encoding to avoid these ranges.
Since you are trying to store binary data in QR codes, you have to
rely only on your own scanner that will handle this binary data. You
don’t have to display text from your QR codes by other software,
like web application at zxing.org, because most QR decoders,
including that of zxing.org use heuristics to detect the character
set used. These heuristics may detect a character set other than
ISO-8859-1 and thus fail to properly display your binary data. Some
scanners use heuristics to detect a character set even if the
character set is explicitly given by ECI. This is why providing ECI
may not help much – scanners still use heuristics even with ECI.
So, using US-ASCII printable characters only (e.g., binary data encoded in Base64 before passing it to a QR Code generator) is the safest choice for QR code against the heuristics. This will also overcome another complication: that ISO-8859-1 was not the default encoding in earlier QR code standard published in 2000 (ISO/IEC 18004:2000). That standard did specify 8-bit Latin/Kana character set in accordance with JIS X 0201 (JIS8 also known as ISO-2022-JP) as default encoding for 8-bit mode, while the updated standard published in 2005 did change the default to ISO-8859-1.
As an alternative to Base-64, you can encode each byte with two hexadecimal characters (0-9, A-F), so, in the QR code your data will be encoded in the alphanumeric mode, not in 8-bit mode. This will disable all heuristics for sure and should not produce larger QR Code than with Base-64, because each character in the alphanumeric mode takes only 6 bits in the QR code stream.
Update:
I recently went back and published the referenced code as a project on GitHub for anyone who wants to use it.
https://github.com/yurelle/Base45Encoder
This is a bit necro, but I just hit this problem, and figured out a solution.
The problem with reading QR Codes with ZXING is that it assumes all QR Payloads are Strings. If you're willing to generate the QR Code in java with ZXING, I developed a solution which enables storing a binary payload in ZXING QR Codes with a storage efficiently loss of only -8%; better than the 33% inflation from Base64.
It exploits an internal compression optimization of the ZXING library based around pure Alphanum Strings. If you want a full explanation, with math and Unit Tests, check out my other answer.
But the short answer is this:
Solution
I implemented it as a self-contained static utility class, so all you have to do is call:
//Encode
final byte[] myBinaryData = ...;
final String encodedStr = BinaryToBase45Encoder.encodeToBase45QrPayload(myBinaryData);
//Decode
final byte[] decodedBytes = BinaryToBase45Encoder.decodeBase45QrPayload(encodedStr);
Alternatively, you can also do it via InputStreams:
//Encode
final InputStream in_1 = ... ;
final String encodedStr = BinaryToBase45Encoder.encodeToBase45QrPayload(in_1);
//Decode
final InputStream in_2 = ... ;
final byte[] decodedBytes = BinaryToBase45Encoder.decodeBase45QrPayload(in_2);
Here's the implementation
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
/**
* For some reason none of the Java QR Code libraries support binary payloads. At least, none that
* I could find anyway. The commonly suggested workaround for this is to use Base64 encoding.
* However, this results in a 33% payload size inflation. If your payload is already near the size
* limit of QR codes, this is a lot.
*
* This class implements an encoder which takes advantage of a built-in compression optimization
* of the ZXING QR Code library, to enable the storage of Binary data into a QR Code, with a
* storage efficiency loss of only -8%.
*
* The built-in optimization is this: ZXING will automatically detect if your String payload is
* purely AlphaNumeric (by their own definition), and if so, it will automatically compress 2
* AlphaNumeric characters into 11 bits.
*
*
* ----------------------
*
*
* The included ALPHANUMERIC_TABLE is the conversion table used by the ZXING library as a reverse
* index for determining if a given input data should be classified as alphanumeric.
*
* See:
*
* com.google.zxing.qrcode.encoder.Encoder.chooseMode(String content, String encoding)
*
* which scans through the input string one character at a time and passes them to:
*
* getAlphanumericCode(int code)
*
* in the same class, which uses that character as a numeric index into the the
* ALPHANUMERIC_TABLE.
*
* If you examine the values, you'll notice that it ignores / disqualifies certain values, and
* effectively converts the input into base 45 (0 -> 44; -1 is interpreted by the calling code
* to mean a failure). This is confirmed in the function:
*
* appendAlphanumericBytes(CharSequence content, BitArray bits)
*
* where they pack 2 of these base 45 digits into 11 bits. This presents us with an opportunity.
* If we can take our data, and convert it into a compatible base 45 alphanumeric representation,
* then the QR Encoder will automatically pack that data into sub-byte chunks.
*
* 2 digits in base 45 is 2,025 possible values. 11 bits has a maximum storage capacity of 2,048
* possible states. This is only a loss of 1.1% in storage efficiency behind raw binary.
*
* 45 ^ 2 = 2,025
* 2 ^ 11 = 2,048
* 2,048 - 2,025 = 23
* 23 / 2,048 = 0.01123046875 = 1.123%
*
* However, this is the ideal / theoretical efficiency. This implementation processes data in
* chunks, using a Long as a computational buffer. However, since Java Long's are singed, we
* can only use the lower 7 bytes. The conversion code requires continuously positive values;
* using the highest 8th byte would contaminate the sign bit and randomly produce negative
* values.
*
*
* Real-World Test:
*
* Using a 7 byte Long to encode a 2KB buffer of random bytes, we get the following results.
*
* Raw Binary Size: 2,048
* Encoded String Size: 3,218
* QR Code Alphanum Size: 2,213 (after the QR Code compresses 2 base45 digits to 11 bits)
*
* This is a real-world storage efficiency loss of only 8%.
*
* 2,213 - 2,048 = 165
* 165 / 2,048 = 0.08056640625 = 8.0566%
*/
public class BinaryToBase45Encoder {
public final static int[] ALPHANUMERIC_TABLE;
/*
* You could probably just copy & paste the array literal from the ZXING source code; it's only
* an array definition. But I was unsure of the licensing issues with posting it on the internet,
* so I did it this way.
*/
static {
final Field SOURCE_ALPHANUMERIC_TABLE;
int[] tmp;
//Copy lookup table from ZXING Encoder class
try {
SOURCE_ALPHANUMERIC_TABLE = com.google.zxing.qrcode.encoder.Encoder.class.getDeclaredField("ALPHANUMERIC_TABLE");
SOURCE_ALPHANUMERIC_TABLE.setAccessible(true);
tmp = (int[]) SOURCE_ALPHANUMERIC_TABLE.get(null);
} catch (NoSuchFieldException e) {
e.printStackTrace();//Shouldn't happen
tmp = null;
} catch (IllegalAccessException e) {
e.printStackTrace();//Shouldn't happen
tmp = null;
}
//Store
ALPHANUMERIC_TABLE = tmp;
}
public static final int NUM_DISTINCT_ALPHANUM_VALUES = 45;
public static final char[] alphaNumReverseIndex = new char[NUM_DISTINCT_ALPHANUM_VALUES];
static {
//Build AlphaNum Index
final int len = ALPHANUMERIC_TABLE.length;
for (int x = 0; x < len; x++) {
// The base45 result which the alphanum lookup table produces.
// i.e. the base45 digit value which String characters are
// converted into.
//
// We use this value to build a reverse lookup table to find
// the String character we have to send to the encoder, to
// make it produce the given base45 digit value.
final int base45DigitValue = ALPHANUMERIC_TABLE[x];
//Ignore the -1 records
if (base45DigitValue > -1) {
//The index into the lookup table which produces the given base45 digit value.
//
//i.e. to produce a base45 digit with the numeric value in base45DigitValue, we need
//to send the Encoder a String character with the numeric value in x.
alphaNumReverseIndex[base45DigitValue] = (char) x;
}
}
}
/*
* The storage capacity of one digit in the number system; i.e. the maximum
* possible number of distinct values which can be stored in 1 logical digit
*/
public static final int QR_PAYLOAD_NUMERIC_BASE = NUM_DISTINCT_ALPHANUM_VALUES;
/*
* We can't use all 8 bytes, because the Long is signed, and the conversion math
* requires consistently positive values. If we populated all 8 bytes, then the
* last byte has the potential to contaminate the sign bit, and break the
* conversion math. So, we only use the lower 7 bytes, and avoid this problem.
*/
public static final int LONG_USABLE_BYTES = Long.BYTES - 1;
//The following mapping was determined by brute-forcing -1 Long (all bits 1), and compressing to base45 until it hit zero.
public static final int[] BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION = new int[] {0,2,3,5,6,8,9,11,12};
public static final int NUM_BASE45_DIGITS_PER_LONG = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION[LONG_USABLE_BYTES];
public static final Map<Integer, Integer> BASE45_TO_BINARY_DIGIT_COUNT_CONVERSION = new HashMap<>();
static {
//Build Reverse Lookup
int len = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION.length;
for (int x=0; x<len; x++) {
int numB45Digits = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION[x];
BASE45_TO_BINARY_DIGIT_COUNT_CONVERSION.put(numB45Digits, x);
}
}
public static String encodeToBase45QrPayload(final byte[] inputData) throws IOException {
return encodeToBase45QrPayload(new ByteArrayInputStream(inputData));
}
public static String encodeToBase45QrPayload(final InputStream in) throws IOException {
//Init conversion state vars
final StringBuilder strOut = new StringBuilder();
int data;
long buf = 0;
// Process all input data in chunks of size LONG.BYTES, this allows for economies of scale
// so we can process more digits of arbitrary size before we hit the wall of the binary
// chunk size in a power of 2, and have to transmit a sub-optimal chunk of the "crumbs"
// left over; i.e. the slack space between where the multiples of QR_PAYLOAD_NUMERIC_BASE
// and the powers of 2 don't quite line up.
while(in.available() > 0) {
//Fill buffer
int numBytesStored = 0;
while (numBytesStored < LONG_USABLE_BYTES && in.available() > 0) {
//Read next byte
data = in.read();
//Push byte into buffer
buf = (buf << 8) | data; //8 bits per byte
//Increment
numBytesStored++;
}
//Write out in lower base
final StringBuilder outputChunkBuffer = new StringBuilder();
final int numBase45Digits = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION[numBytesStored];
int numB45DigitsProcessed = 0;
while(numB45DigitsProcessed < numBase45Digits) {
//Chunk out a digit
final byte digit = (byte) (buf % QR_PAYLOAD_NUMERIC_BASE);
//Drop digit data from buffer
buf = buf / QR_PAYLOAD_NUMERIC_BASE;
//Write Digit
outputChunkBuffer.append(alphaNumReverseIndex[(int) digit]);
//Track output digits
numB45DigitsProcessed++;
}
/*
* The way this code works, the processing output results in a First-In-Last-Out digit
* reversal. So, we need to buffer the chunk output, and feed it to the OutputStream
* backwards to correct this.
*
* We could probably get away with writing the bytes out in inverted order, and then
* flipping them back on the decode side, but just to be safe, I'm always keeping
* them in the proper order.
*/
strOut.append(outputChunkBuffer.reverse().toString());
}
//Return
return strOut.toString();
}
public static byte[] decodeBase45QrPayload(final String inputStr) throws IOException {
//Prep for InputStream
final byte[] buf = inputStr.getBytes();//Use the default encoding (the same encoding that the 'char' primitive uses)
return decodeBase45QrPayload(new ByteArrayInputStream(buf));
}
public static byte[] decodeBase45QrPayload(final InputStream in) throws IOException {
//Init conversion state vars
final ByteArrayOutputStream out = new ByteArrayOutputStream();
int data;
long buf = 0;
int x=0;
// Process all input data in chunks of size LONG.BYTES, this allows for economies of scale
// so we can process more digits of arbitrary size before we hit the wall of the binary
// chunk size in a power of 2, and have to transmit a sub-optimal chunk of the "crumbs"
// left over; i.e. the slack space between where the multiples of QR_PAYLOAD_NUMERIC_BASE
// and the powers of 2 don't quite line up.
while(in.available() > 0) {
//Convert & Fill Buffer
int numB45Digits = 0;
while (numB45Digits < NUM_BASE45_DIGITS_PER_LONG && in.available() > 0) {
//Read in next char
char c = (char) in.read();
//Translate back through lookup table
int digit = ALPHANUMERIC_TABLE[(int) c];
//Shift buffer up one digit to make room
buf *= QR_PAYLOAD_NUMERIC_BASE;
//Append next digit
buf += digit;
//Increment
numB45Digits++;
}
//Write out in higher base
final LinkedList<Byte> outputChunkBuffer = new LinkedList<>();
final int numBytes = BASE45_TO_BINARY_DIGIT_COUNT_CONVERSION.get(numB45Digits);
int numBytesProcessed = 0;
while(numBytesProcessed < numBytes) {
//Chunk out 1 byte
final byte chunk = (byte) buf;
//Shift buffer to next byte
buf = buf >> 8; //8 bits per byte
//Write byte to output
//
//Again, we need to invert the order of the bytes, so as we chunk them off, push
//them onto a FILO stack; inverting their order.
outputChunkBuffer.push(chunk);
//Increment
numBytesProcessed++;
}
//Write chunk buffer to output stream (in reverse order)
while (outputChunkBuffer.size() > 0) {
out.write(outputChunkBuffer.pop());
}
}
//Return
out.flush();
out.close();
return out.toByteArray();
}
}
Just at a glance, the qr formats are different. I'd compare the qr formats to see if it's a problem of error correction or encoding or something else.
It turned out that ZXing is just crap, and ZBar does some weird stuff with the data (converting it to UTF-8 for example). I managed to get it to output the raw data including null bytes though. Here is a patch for the best Android ZBar library I found, that has now been merged.
I used System.Convert.ToBase64String to convert the supplied sample byte array into a Base64-encoded string, then I used ZXing to create a QRCode image.
Next I called ZXing to read the string back from the generated QRCode, and then called System.Convert.FromBase64String to convert the string back into a byte array.
I confirm that the data completed the round trip successfully.
The informational RFC 9285 - The Base45 Data Encoding document describing the optimal scheme for storing binary data within the constraints of QR Alphanumeric Mode was recently published by the IETF.
(one positive side-effect of ongoing standardization work surrounding Health Certificate QR-codes)
I want to store a password (no hash) on my disk. it's nothing sensitive but i just don't want it in plaintext on my disk.
what i tried till now is:
converting the string in binary and XOR it with the binary of a key.
bool ok = true;
QByteArray qbaPW("mypass");
long long intPW = qbaPW.toHex().toLongLong( &ok, 16 );
QString binPW = QString::number( intPW, 2);
but the thing is, that it only works with short passwords. if they are too long intPW gets too big for longlong. any ideas how can avoid that thing?
cheers
A QByteArray is like a char array[len] in C. You can access individual members and do whatever you please with them. For example:
QByteArray const key("mykey");
QByteArray password("password");
for (int ik = 0, ip = 0;
ip < password.length();
++ ip, ik = (ik+1 < key.length() ? ik+1 : 0)) {
password[ip] = password[ip] ^ key[ik];
}
Since this just XORs with the key, you repeat this procedure to decrypt the password. A good key will be generated randomly and will be longer than the longest password you envisage (say 64 characters).
Do note that this method is only reasonably safe if the users are explicitly informed not to reuse any other password in your application - otherwise you're essentially leaking passwords that are supposed to be secure.
I have a binary data stream which contains data that should be interpreted as a Qstring. Starting from the third byte. Here is how the package is generated (on a client).
QByteArray package;
package.append( QByteArray::fromHex("0002") ); // First two bytes
package.append( "filename.txt" ); // String of undefined size
package.append( QByteArray::fromHex("00")); // End of string
The decoding is done on a different machine (server). I would like to get a Qstring of value "filename.txt" from the QByteArray package without relying on the size of the string (since the server doesn't have that information) but on the string terminator 00. How can this be achieved?
Since this decoding will be done on a different machine, how should the raw data be generated on the client to avoid problems with endianess?
You should wrap the QByteArray in a QDataStream so you can specify the endianess explicitly and make use of the stream operators
QByteArray package;
QDataStream stream(package, QIODevice::WriteOnly);
stream.setByteOrder( QDataStream::BigEndian);
stream << static_cast<quint16>(0x0002); // First two bytes
stream << "filename.txt"; // String of undefined size
// no need to write terminating 0 because data stream will prepend length
then you can read in the other direction:
QByteArray package;
QDataStream stream(package, QIODevice::WriteOnly);
stream.setByteOrder( QDataStream::BigEndian);
quint16 id;
stream >> id; // First two bytes
char* filename;
stream >> filename; // String of undefined size
QString file = QString.fromLatin1(filename);
delete[] filename; //cleanup
or you can pass a QString to the stream in the first place and not need to deal with the char array:
QByteArray package;
QDataStream stream(package, QIODevice::WriteOnly);
stream.setByteOrder( QDataStream::BigEndian);
stream << static_cast<quint16>(0x0002); // First two bytes
stream << QStringLiteral("filename.txt"); // String of undefined size
note that this will write in utf16 meaning it is unicode enabled
the serialization format is documented at http://qt-project.org/doc/qt-5.0/qtcore/datastreamformat.html