cryptest

commit 531149cecf7ba7aad2d3e8594bd61f5bf50de3c7
parent 37942803e44b642ae449f35cc5e03bd59fcfda5e
Author: finwo <finwo@pm.me>
Date:   Thu, 10 Aug 2017 19:28:31 +0200

functional

Diffstat:
M
inc/base.h
 | 
3
+++
M
src/decrypt.c
 | 
35
+++++++++++++++++++++++++++++++++++
M
src/encrypt.c
 | 
70
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3 files changed, 108 insertions(+), 0 deletions(-)
diff --git a/inc/base.h b/inc/base.h
@@ -2,6 +2,9 @@
 extern "C" {
 #endif
 
+#define MIN(a,b) (((a)<(b))?(a):(b))
+#define MAX(a,b) (((a)>(b))?(a):(b))
+
 unsigned int atoui( char *in );
 
 int encrypt( unsigned int mult, unsigned int modulo, unsigned int padding );
diff --git a/src/decrypt.c b/src/decrypt.c
@@ -2,10 +2,45 @@
 extern "C" {
 #endif
 
+#include <stdio.h>
+
 #include "base.h"
 
 int decrypt( unsigned int mult, unsigned int modulo, unsigned int padding ) {
 
+  // Initialize variables
+  unsigned long long seed = 0;
+  unsigned long long obuf = 0;
+  int obuf_len = 0;
+  int i, c;
+
+  // Read padding & build seed
+  padding--;
+  seed = fgetc(stdin);
+  while( padding-- ) {
+    seed = seed * mult;
+    seed = seed % modulo;
+    c = (seed%256) ^ fgetc(stdin);
+    seed ^= c;
+  }
+
+  while( 1 ) {
+    c = fgetc(stdin);
+    if(c==EOF) break;
+    seed *= mult;    
+    seed += c;
+    seed = seed % modulo;
+    obuf = obuf << 7;
+    obuf &= ~127;
+    obuf |= seed%128;
+    obuf_len += 7;
+    if(obuf_len>=8) {
+      fputc( (obuf>>(obuf_len-8))%256, stdout );
+      obuf_len-=8;
+    }
+  }
+  
+  return 0;
 }
 
 #ifdef __cplusplus
diff --git a/src/encrypt.c b/src/encrypt.c
@@ -2,10 +2,80 @@
 extern "C" {
 #endif
 
+#include <stdio.h>
+
 #include "base.h"
 
 int encrypt( unsigned int mult, unsigned int modulo, unsigned int padding ) {
 
+  // Initialize variables
+  unsigned long long seed     = 0;
+  unsigned long long ibuf     = 0;
+  int flags = 2; // 1=running, 2=input
+  int c,e, ibuf_len = 0;
+
+  // Randomize the 'rand' call
+  srandom((unsigned)time(NULL));
+  for( seed = 5000; seed; rand(), seed-- );
+
+  // Ensure padding
+  while( padding-- ) {
+    if ( flags & 1 ) {
+      seed = seed * mult;
+      seed = seed % modulo;
+      seed = seed ^ ( random() % 256 );
+      fputc( seed % 256, stdout );
+    } else {
+      seed = random() % 256;
+      fputc( seed, stdout );
+      flags |= 1;
+    }
+  }
+
+  // Start encoding
+  while( flags & 1 ) {
+
+    // Handle stdin
+    if ( ( flags & 2 ) && ( ibuf_len < 7 ) ) {
+      if ( (c=fgetc(stdin)) == EOF ) {
+        flags &= ~2;
+      } else {
+        ibuf = ibuf << 8;
+        ibuf &= ~255;
+        ibuf |= c;
+        ibuf_len += 8;
+      }
+    }
+
+    // Pre-step seed
+    seed *= mult;
+
+    // Fetch input
+    c = ( (ibuf%(1<<ibuf_len)) << 7 ) >> ibuf_len;
+    ibuf_len -= 7;
+
+    // Try the fast method
+    e = ( ((seed+c)%modulo)%128 ) - c;
+
+    // Feedback-based encoding
+    if( ( (seed+e)%modulo)%128 != c ) {
+      e = 0;
+      while( ( (seed+e)%modulo)%128 != c ) e++;
+    }
+    
+    // Output
+    fputc( e, stdout );
+
+    // Post-step seed
+    seed = (seed+e)%modulo;
+
+    // EOF detection
+    if( ibuf_len <= 0 && !(flags&2) ) {
+      flags &= ~1;
+    }
+  }
+
+  return 0;
 }
 
 #ifdef __cplusplus