[OpenSSL] EC_POINT example source

#include <openssl/crypto.h>
#include "ec_lcl.h"

BIGNUM *EC_POINT_point2bn(const EC_GROUP *group,
                          const EC_POINT *point,
                          point_conversion_form_t form,
                          BIGNUM *ret,
                          BN_CTX *ctx)
{
    size_t        buf_len=0;
    unsigned char *buf;

    buf_len = EC_POINT_point2oct(group, point, form, NULL, 0, ctx);


    if (buf_len == 0)
        return NULL;

    if ((buf = OPENSSL_malloc(buf_len)) == NULL)
        return NULL;

    if (!EC_POINT_point2oct(group, point, form, buf, buf_len, ctx))
    {
        OPENSSL_free(buf);
        return NULL;
    }

    ret = BN_bin2bn(buf, buf_len, ret);

    OPENSSL_free(buf);

    return ret;
}

EC_POINT *EC_POINT_bn2point(const EC_GROUP *group,
                            const BIGNUM *bn,
                            EC_POINT *point,
                            BN_CTX *ctx)
{
    size_t        buf_len=0;
    unsigned char *buf;
    EC_POINT      *ret;

    if ((buf_len = BN_num_bytes(bn)) == 0) return NULL;
    buf = OPENSSL_malloc(buf_len);
    if (buf == NULL)
        return NULL;

    if (!BN_bn2bin(bn, buf))
    {
        OPENSSL_free(buf);
        return NULL;
    }

    if (point == NULL)
    {
        if ((ret = EC_POINT_new(group)) == NULL)
        {
            OPENSSL_free(buf);
            return NULL;
        }
    }
    else
        ret = point;

    if (!EC_POINT_oct2point(group, ret, buf, buf_len, ctx))
    {
        if (point == NULL)
            EC_POINT_clear_free(ret);
        OPENSSL_free(buf);
        return NULL;
    }

    OPENSSL_free(buf);
    return ret;
}

static const char *HEX_DIGITS = "0123456789ABCDEF";

/* the return value must be freed (using OPENSSL_free()) */
char *EC_POINT_point2hex(const EC_GROUP *group,
                         const EC_POINT *point,
                         point_conversion_form_t form,
                         BN_CTX *ctx)
{
    char          *ret, *p;
    size_t        buf_len=0,i;
    unsigned char *buf, *pbuf;

    buf_len = EC_POINT_point2oct(group, point, form, NULL, 0, ctx);
    if (buf_len == 0)
        return NULL;

    if ((buf = OPENSSL_malloc(buf_len)) == NULL)
        return NULL;

    if (!EC_POINT_point2oct(group, point, form, buf, buf_len, ctx))
    {
        OPENSSL_free(buf);
        return NULL;
    }

    ret = (char *)OPENSSL_malloc(buf_len*2+2);
    if (ret == NULL)
    {
        OPENSSL_free(buf);
        return NULL;
    }
    p = ret;
    pbuf = buf;
    for (i=buf_len; i > 0; i--)
    {
        int v = (int) *(pbuf++);
        *(p++)=HEX_DIGITS[v>>4];
        *(p++)=HEX_DIGITS[v&0x0F];
    }
    *p='\0';

    OPENSSL_free(buf);

    return ret;
}

EC_POINT *EC_POINT_hex2point(const EC_GROUP *group,
                             const char *buf,
                             EC_POINT *point,
                             BN_CTX *ctx)
{
    EC_POINT *ret=NULL;
    BIGNUM   *tmp_bn=NULL;

    if (!BN_hex2bn(&tmp_bn, buf))
    return NULL;

    ret = EC_POINT_bn2point(group, tmp_bn, point, ctx);

    BN_clear_free(tmp_bn);

    return ret;
}