(3,5) Shamir Secret Sharing

[Rafael Cividanes]

  Hi,

 

    I've implemented (in C++) a simple form of shamir secret sharing for the particular case (3,5). One function receives a BIGNUM A0 an generates the 5 secrets. Another function, receives 3 secrets and generates the recover BIGNUM A0. It's working fine.

 

    The problem is that I need to convert a RSA private key into a BIGNUM A0, and I'm having trouble with this.

 

     I was trying to do this (part of my code):

 

        RSA *Ch_Ap

        unsigned char *buffer, *next;

        BIGNUM *sec_BN = BN_new();

        Ch_Ap = RSA_generate_key(2048, RSA_F4, NULL, 0);

        int size = i2d_RSAPrivateKey(Ch_Ap, 0);

        buffer = next =(unsigned char *)malloc(size);
        i2d_RSAPrivateKey(Ch_Ap, &next);
        BN_bin2bn(buffer, size, sec_BN); 

 

     However, when I use sec_BN in my functions, the recovered BIGNUM is not the same as sec_BN. When I pass another BIGNUM, for example using the function BN_rand_range(), then the recovered BIGNUM is equal (proving that my secret sharing functions is ok).

 

      I think it can be something about Big-Endian conversion in sec_BN, but I didn't find a way to do this conversion and I don't know if it is necessary too.

 

 

       Thanks in advance,

 

 

                Rafael Cividanes.

 

 

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