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# 1  
Old 09-24-2012
Segmentation fault when debugging in C
Dear all,

Currently I am implementing ECC protocols. I used tinyECC package to port ecc to contiki os. This giving me a segmentation fault.

I followed some article Debugging Segmentation Faults and Pointer Problems - Cprogramming.com but I failed to detect the error. Please help me to find that error. Here is my code(part of a code). Error happens in NN_Encode function.

this is some errors occur when debugging

Program received signal SIGSEGV, Segmentation fault.
0x080484c4 in ecc_point2octet (octet=0x80485d0 "UWVS\350i", octet_len=73 'I',
P=0x804a040, compress=0) at octtest.c:108
108 octet[0] = 0x04;

(gdb) info s
#0 0x080484c4 in ecc_point2octet (octet=0x80485d0 "UWVS\350i",
octet_len=73 'I', P=0x804a040, compress=0) at octtest.c:108
#1 0x080485c5 in main () at octtest.c:133

Code:
#include <stdio.h>
#include <stdint.h>
typedef uint32_t NN_DIGIT;
typedef uint64_t NN_DOUBLE_DIGIT;

/* Types for length */
typedef uint8_t NN_UINT;
typedef uint16_t NN_UINT2;

#if defined (SECP128R1) || defined (SECP128R2)
#define KEY_BIT_LEN 128
#else 
#if defined (SECP160K1) || defined (SECP160R1) || defined (SECP160R2) 
#define KEY_BIT_LEN 160
#else 
#if defined (SECP192K1) || defined (SECP192R1)
#define KEY_BIT_LEN 192
#else
#define KEY_BIT_LEN 128
#endif /* 192 */
#endif /* 160 */
#endif /* 128 */

/* Length of digit in bits */
#define NN_DIGIT_BITS 32

/* Length of digit in bytes */
#define NN_DIGIT_LEN (NN_DIGIT_BITS/8)

/* Maximum value of digit */
#define MAX_NN_DIGIT 0xffffffff

/* Number of digits in key
 * used by optimized mod multiplication (ModMultOpt) and optimized mod square (ModSqrOpt)
 *
 */
#define KEYDIGITS (KEY_BIT_LEN/NN_DIGIT_BITS) //5

/* Maximum length in digits */
#define MAX_NN_DIGITS (KEYDIGITS+1)

/* buffer size
 *should be large enough to hold order of base point
 */
#define NUMWORDS MAX_NN_DIGITS

/* the mask for ModSqrOpt */
#define MOD_SQR_MASK1 0x8000000000000000ll
#define MOD_SQR_MASK2 0x0000000100000000ll

typedef struct Point
{
    // point's coordinates
    NN_DIGIT x[NUMWORDS];
    NN_DIGIT y[NUMWORDS];
} Point;

Point pbkey_alice;
void 
NN_Encode(unsigned char *a, NN_UINT len, NN_DIGIT *b, NN_UINT digits)
{
  NN_DIGIT t;
  int j;
  unsigned int i, u;

  for(i = 0, j = len - 1; i < digits && j >= 0; i++) {
    t = b[i];
    for(u = 0; j >= 0 && u < NN_DIGIT_BITS; j--, u += 8) {
      a[j] = (unsigned char)(t >> u);
    }
  }

  for(; j >= 0; j--) {
    a[j] = 0;
  }
}

int ecc_point2octet(uint8_t *octet, NN_UINT octet_len, Point *P, int compress)
{
	if (compress){
		if(octet_len < KEYDIGITS*NN_DIGIT_LEN+1)
	  {//too small octet
		return -1;
    }
    else
    {
		  //compressed point representation
			if((1 & P->y[0]) == 0){
	  	octet[0] = 0x02;
			}
			else
				{
	  			octet[0] = 0x03;
				}
			NN_Encode(octet+1, KEYDIGITS*NN_DIGIT_LEN, P->x, KEYDIGITS);
			return KEYDIGITS*NN_DIGIT_LEN+1;
      }
	}
  else
  {//non compressed
	 if(octet_len < 2*KEYDIGITS*NN_DIGIT_LEN+1)
    {
    
		return -1;
    }
    else
    {
			octet[0] = 0x04;
			NN_Encode(octet+1, KEYDIGITS*NN_DIGIT_LEN, P->x, KEYDIGITS);
			NN_Encode(octet+1+KEYDIGITS*NN_DIGIT_LEN, KEYDIGITS*NN_DIGIT_LEN, P->y, KEYDIGITS);
			return 2*KEYDIGITS*NN_DIGIT_LEN+1;
		}
  }
}

int main()
{
pbkey_alice.x[5] = 0x00000000;
  pbkey_alice.x[4] = 0x21961f69;
  pbkey_alice.x[3] = 0xf02d202b;
  pbkey_alice.x[2] = 0xa4b41f1a;
  pbkey_alice.x[1] = 0x0aa08a86;
  pbkey_alice.x[0] = 0xdf27908d;
    
  pbkey_alice.y[5] = 0x00000000;
  pbkey_alice.y[4] = 0x378e1278;
  pbkey_alice.y[3] = 0x62836d75;
  pbkey_alice.y[2] = 0x7acb7ca4;
  pbkey_alice.y[1] = 0x0dc0ad13;
  pbkey_alice.y[0] = 0x741e287c;
uint8_t *C;
int C_len = 2*KEYDIGITS*NN_DIGIT_LEN + 1 + 20 + 20;
int oct_len = ecc_point2octet(C, C_len, &pbkey_alice, 0);

}

# 2  
Old 09-24-2012
Let's start in main(). You initialize six elements of two arrays each of which are allocated five elements. (pbkey_alice is an object of type Point which is defined by:
Code:
typedef struct Point
{
    // point's coordinates
    NN_DIGIT x[NUMWORDS];
    NN_DIGIT y[NUMWORDS];
} Point;

Point pbkey_alice;

which after one round of evaluating macros expands to:
Code:
typedef struct Point
{
    // point's coordinates
    uint32_t x[MAX_NN_DIGITS];
    uint32_t y[MAX_NN_DIGITS];
} Point;

Point pbkey_alice;

and then MAX_NN_DIGITS which expands to (KEYDIGITS+1) which expands to ((KEY_BIT_LEN/NN_DIGIT_BITS)+1) (with a comment saying that KEY_BIT_LEN/NN_DIGIT_BITS is 5) which (since none of the following are defined: SECP128R1, SECP128R2, SECP160K1, SECP160R1, SECP160R2, SECP192K1, and SECP192R1) expands to ((128/32)+1) (note that 128/32 is 4; not 5) which finally evaluates to:
Code:
]typedef struct Point
{
    // point's coordinates
    uint32_t x[5];
    uint32_t y[5];
} Point;

Point pbkey_alice;

If you start off in main() writing into unallocated areas, you should expect that something bad is going to happen.

Then you allocate a pointer uint8_t *C; but do not initialize it. You then pass this uninitialized pointer to ecc_point2octet() which then stores data into the byte pointed to by this uninitialized pointer and then calls NN_Encode() to store more data into subsequent bytes using the same uninitialized pointer. Storing data into areas pointed to by uninitialized (or corrupted) pointers is a very common way to get a segmentation fault.

You're on your own from here.
This User Gave Thanks to Don Cragun For This Post:
chap
# 3  
Old 09-24-2012
MySQL
First of all thanks very much for your explanation, I did most of them blindly. I initialized C and it works now. Smilie
uint8_t *C = malloc(sizeof(uint8_t));

thanks in advance
# 4  
Old 09-24-2012
Quote:
Originally Posted by chap
First of all thanks very much for your explanation, I did most of them blindly. I initialized C and it works now. Smilie
uint8_t *C = malloc(sizeof(uint8_t));

thanks in advance
That is not sufficient. You need at least (C_len * sizeof(uint8_t)) bytes, and C_len isn't defined yet where you're initializing C.

Did you fix the fact that you're putting more data into pbkey_alice than it is allocated to hold?
This User Gave Thanks to Don Cragun For This Post:
chap
# 5  
Old 09-24-2012
in actual case I am using KEY_BIT_LEN as 160, and I used C_len like this
C_len = 2*KEYDIGITS*NN_DIGIT_LEN + 1 + 20 + 20; and use it in function,,,something wrong with it?

and I can't understand "Did you fix the fact that you're putting more data into pbkey_alice than it is allocated to hold?" I think I'm not. could you explain it to me?
# 6  
Old 09-24-2012
Quote:
Originally Posted by chap
in actual case I am using KEY_BIT_LEN as 160, and I used C_len like this
C_len = 2*KEYDIGITS*NN_DIGIT_LEN + 1 + 20 + 20; and use it in function,,,something wrong with it?

and I can't understand "Did you fix the fact that you're putting more data into pbkey_alice than it is allocated to hold?" I think I'm not. could you explain it to me?
As I explained in my first message on this thread, the source you showed us sets KEY_BIT_LEN to 128; not to 160.

You said you initialize C using the statement:
Code:
uint8_t *C = malloc(sizeof(uint8_t));

which initializes C to be a pointer to a buffer with space to hold 1 byte.
You then pass that pointer to
Code:
ecc_point2octet(C, C_len, &pbkey_alice, 0);

telling it that C is a pointer to a buffer containing 2*KEYDIGITS*NN_DIGIT_LEN + 1 + 20 + 20 bytes.

Do you not see that there is a problem when you tell ecc_point2octet() you are passing it a pointer to a buffer containing 73 bytes when you pass it a pointer to a buffer that has only been allocated 1 byte?
This User Gave Thanks to Don Cragun For This Post:
chap
# 7  
Old 09-24-2012
yeah,,something wrong, I'm getting an another error

---------- Post updated at 09:59 PM ---------- Previous update was at 09:37 PM ----------

in nesc code it use like this
uint8_t C[2*KEYDIGITS*NN_DIGIT_LEN + 1 + 20 + 20];

so I used like this,,,can we use like this? 73* 1 bytes?
int xxx = 2*KEYDIGITS*NN_DIGIT_LEN + 1 + 20+ 20;
uint8_t *C = malloc(xxx*sizeof(uint8_t));
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