Re: Base32Decoder and custom alphabet

[oe]

Am Freitag, 19. November 2010 16:11:42 UTC+1 schrieb Olivier Ruskovini:
>
> Hello, 
>
> I would like to use custom BASE32 alphabet with Base32Decoder class 
> but my code doesn't work, it crashes cause of an inifinite Loop : 
>
> CryptoPP::Base32Decoder decoder; 
> static int decodingArray[256]; 
> static const byte myAlphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"; 
>
> CryptoPP::Base32Decoder::InitializeDecodingLookupArray(decodingArray,myAlphabet,
>  
>
> 32,true); 
> b32_decoder.Initialize(CryptoPP::MakeParameters(CryptoPP::Name::DecodingLookupArray(),
>  
>
> (const int *)decodingArray, false)); 
>
>
> It crashes here in "Initialize function" cause of an infinite loop (i 
> have checked this with a debugger). 
>
> Any idea? 
>
> Thanx. 
>
 
 Hello, 
 
I've also been trying to use CryptoPP::Base32Decoder with a custom
alphabet (for interop with Python's base64 module) and ran into the same
issue as OP.  Here's my SSCCE, using Crypto++ 5.6.2: 
 
#include <iostream> 
#include <memory> 
#include <string> 
 
#include <cryptopp/base32.h> 
#include <cryptopp/filters.h> 
 
using namespace std; 
using namespace CryptoPP; 
 
byte const g_base32Alphabet[32 + 1] = 
   "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"; 
int g_base32Lookup[256]; 
 
int 
main() 
{ 
   Base32Decoder::InitializeDecodingLookupArray 
      (g_base32Lookup, g_base32Alphabet, 32, /*caseInsensitive*/ false); 
 
   string const b32Text("NF2CA53POJVXGII="); 
   string text; 
 
   auto_ptr<Base32Decoder> 
      b32dec(new Base32Decoder(new StringSink(text))); 
   b32dec->Initialize 
      (MakeParameters(Name::DecodingLookupArray(), 
                      static_cast<int const *>(&g_base32Lookup[0])), 
       0); 
   StringSource(b32Text, /*pumpAll*/ true, b32dec.release()); 
 
   cout << text << endl; 
} 
 
The call to b32dec->Initialize() segfaults, due to a stack overflow
(gdb backtrace): 
 
[...] 
#174689 0x0804d183 in CryptoPP::Base32Decoder::IsolatedInitialize 
(this=0x81aa050, parameters=...) at base32.cpp:23 
#174690 0x080b8667 in CryptoPP::Filter::Initialize (this=0x81aa050, 
parameters=..., propagation=-1) at filters.cpp:64 
#174691 0x0804d183 in CryptoPP::Base32Decoder::IsolatedInitialize 
(this=0x81aa050, parameters=...) at base32.cpp:23 
#174692 0x080b8667 in CryptoPP::Filter::Initialize (this=0x81aa050, 
parameters=..., propagation=-1) at filters.cpp:64 
#174693 0x0804d183 in CryptoPP::Base32Decoder::IsolatedInitialize 
(this=0x81aa050, parameters=...) at base32.cpp:23 
#174694 0x080b8667 in CryptoPP::Filter::Initialize (this=0x81aa050, 
parameters=..., propagation=-1) at filters.cpp:64 
#174695 0x0804a28f in main () at demo.cc:29 
 
The problem seems to be that Base32Decoder::IsolatedInitialize() calls 
BaseN_Decoder::Initialize() (instead of IsolatedInitialize()?) which in 
turn calls IsolatedInitialize() again and so forth.. 
 
With the following patch things seem to work as expected then: 
 
diff -ru cryptopp562/base32.cpp cryptopp562.new/base32.cpp 
--- cryptopp562/base32.cpp    2009-03-01 19:44:04.000000000 +0100 
+++ cryptopp562.new/base32.cpp    2014-09-12 12:04:45.000000000 +0200 
@@ -18,7 +18,7 @@ 
  
 void Base32Decoder::IsolatedInitialize(const NameValuePairs &parameters) 
 { 
-    BaseN_Decoder::Initialize(CombinedNameValuePairs( 
+    BaseN_Decoder::IsolatedInitialize(CombinedNameValuePairs( 
         parameters, 
         MakeParameters(Name::DecodingLookupArray(), 
GetDefaultDecodingLookupArray(), false)(Name::Log2Base(), 5, true))); 
 } 
 
Anyhow, that's what I came up with but maybe someone in the know can shed 
some (more) light. 
 
Thanks and regards 
Oliver 

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#include <iostream>
#include <memory>
#include <string>

#include <cryptopp/base32.h>
#include <cryptopp/filters.h>

using namespace std;
using namespace CryptoPP;

byte const g_base32Alphabet[32 + 1] =
   "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
int g_base32Lookup[256];

int
main()
{
   Base32Decoder::InitializeDecodingLookupArray
      (g_base32Lookup, g_base32Alphabet, 32, /*caseInsensitive*/ false);

   string const b32Text("NF2CA53POJVXGII=");
   string text;

   auto_ptr<Base32Decoder>
      b32dec(new Base32Decoder(new StringSink(text)));
   b32dec->Initialize
      (MakeParameters(Name::DecodingLookupArray(),
                      static_cast<int const *>(&g_base32Lookup[0])),
       0);
   StringSource(b32Text, /*pumpAll*/ true, b32dec.release());

   cout << text << endl;
}


diff -ru cryptopp562/base32.cpp cryptopp562.new/base32.cpp
--- cryptopp562/base32.cpp	2009-03-01 19:44:04.000000000 +0100
+++ cryptopp562.new/base32.cpp	2014-09-12 12:04:45.000000000 +0200
@@ -18,7 +18,7 @@
 
 void Base32Decoder::IsolatedInitialize(const NameValuePairs &parameters)
 {
-	BaseN_Decoder::Initialize(CombinedNameValuePairs(
+	BaseN_Decoder::IsolatedInitialize(CombinedNameValuePairs(
 		parameters,
 		MakeParameters(Name::DecodingLookupArray(), GetDefaultDecodingLookupArray(), false)(Name::Log2Base(), 5, true)));
 }