DES decryption issue

Question

I am using DES decryption with ECB mode. I am using the following code for decryption :

NSString *token = @"kRAz86UoZd5tFKf0xv8TKg==";
NSString *key = @"meristem";

const void *vplainText;
size_t plainTextBufferSize;

NSData *EncryptData = [[NSData alloc] initWithBase64EncodedString:token options:0];
plainTextBufferSize = [EncryptData length];
vplainText = [EncryptData bytes];

//plainTextBufferSize = [token length];
//vplainText = (const void *) [token UTF8String];

CCCryptorStatus ccStatus;
uint8_t *bufferPtr = NULL;
size_t bufferPtrSize = 0;
size_t movedBytes;

bufferPtrSize = (plainTextBufferSize + kCCBlockSize3DES) & ~(kCCBlockSize3DES - 1);
bufferPtr = malloc( bufferPtrSize * sizeof(uint8_t));
memset((void *)bufferPtr, 0x0, bufferPtrSize);

NSString *initVec = @"init Vec";
const void *vkey = (const void *) [key UTF8String];
const void *vinitVec;
vinitVec = (const void *) [initVec UTF8String];

ccStatus = CCCrypt(kCCDecrypt,
                   kCCAlgorithmDES,
                   kCCOptionPKCS7Padding | kCCOptionECBMode,
                   vkey, //"123456789012345678901234", //key
                   kCCKeySizeDES,
                   NULL,// vinitVec, //"init Vec", //iv,
                   vplainText, //"Your Name", //plainText,
                   plainTextBufferSize,
                   (void *)bufferPtr,
                   bufferPtrSize,
                   &movedBytes);

NSData *myData = [NSData dataWithBytes:(const void *)bufferPtr length:(NSUInteger)movedBytes];
NSString *decodedString = [[NSString alloc] initWithData:myData encoding:NSUTF8StringEncoding];
NSLog(@"dis is data %@",decodedString);

Here, you can see that my encrypted string is kRAz86UoZd5tFKf0xv8TKg== and its result is vishal thakur. But by using the above code for decryption, I am getting only vishal t. I cant understand why am not getting the full string. Please can anyone tell me what I am doing wrong.

Try more bigger buffer for result. – Cy-4AH Feb 04 '14 at 12:00 — Cy-4AH, Feb 04 '14 at 12:00
@Cy-4AH Can u please tell me how can I do? – Sudha Tiwari Feb 04 '14 at 12:06 — Sudha Tiwari, Feb 04 '14 at 12:06

score 2 · Answer 1 · answered Feb 04 '14 at 13:22

2

I have solved my issue by replacing this line

plainTextBufferSize = [EncryptData length];

into

plainTextBufferSize = [EncryptData length]+1;

answered Feb 04 '14 at 13:22

Sudha Tiwari

2,499
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0xKayvan · Accepted Answer · 2014-02-04T13:29:08.380

1

Edited: I think it has something to do with plainTextBufferSize, and this cause the problem as you call it in your CCCrypt function.

Try changing its value before CCCrypt function.

edited Feb 04 '14 at 13:29

answered Feb 04 '14 at 12:16

0xKayvan

368
1
4
18

1

no luck! :( but I soved out the problem by changing this line plainTextBufferSize = [EncryptData length]; into plainTextBufferSize = [EncryptData length]+1; And thanks a lot!! – Sudha Tiwari Feb 04 '14 at 12:51
You're welcome. (I didn't see that line of the code! `plainTextBufferSize = [EncryptData length];` :D) I knew the problem was with `plainTextBufferSize`, but as I didn't notice that line, my first answer was totally wrong, as any value you assign to `plainTextBufferSize` would be replaced with `[EncryptData length]`. I edited my answer to be no longer misleading. – 0xKayvan Feb 04 '14 at 13:10
and as a suggestion: answer your own question and accept the answer for others who may have this problem. ;) – 0xKayvan Feb 04 '14 at 13:13

DES decryption issue

2 Answers2