To: linux-kernel@vger.kernel.org, linux-c-programming@vger.kernel.org
Subject: Problem in encryption in kernel
Reply-To: vintya@excite.com
From: "Vineet Joglekar" <vintya@excite.com>
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Message-Id: <20050321221648.169188AECF@xprdmailfe2.nwk.excite.com>
Date: Mon, 21 Mar 2005 17:16:48 -0500 (EST)
Sender: linux-kernel-owner@vger.kernel.org
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Hi all,

I am trying to use some encryption routines inside the kernel (2.4.28). I have done the following things, please let me know where I am going wrong, or anything additional needs to be done.

1: defined struct crypto_tfm * tfm and allocated to des using crypto_alloc_tfm()
2: called crypto_cipher_setkey() to set the DES key.
3: defined the ecryption function as follows:

int encrypt(char *buffer, size_t buffer_length)
{
    struct scatterlist sg;
    int ret = 0,i = 0;

    printk("addr sent = %x\n",buffer);
    sg.page = virt_to_page(buffer);
    printk("addr frm virt_to_page = %x\n",sg.page);
// these 2 address are coming out to be different.

    sg.length = 8;
    for(i=0; i < buffer_length; i+=8)
    {
        sg.offset = i;

        ret = crypto_cipher_encrypt(tfm,&sg,&sg,8);
        if(ret) printk("error");
    }
    return ret;
}

Now if I define a character array temp[16], pass it to encrypt as encrypt(temp,16) and on the next line, if I see the the array using printk again, it doesnt show it as encrypted. whats going wrong? (it didnt give any memory fault that this point, maybe it encrypted something else - as the address I saw were different)

I tried to see the address in pointer "buffer" and address returned by "virt_to_page", they are different.

Since the addresses were different, I tried to do following variations, but it always gave some memory fault:
1: instead of using sg.page, i tried to use sg.address as
sg.address = buffer; sg.offset = i;
2 : I tried to assign sg.page = buffer (w/o using virt_to_page) and sg.offset = i;
3: I tried
        sg.page = virt_to_page(buffer);
        sg.offset = ((unsigned long)buffer + ~PAGE_MASK) + i;

So I am stuck and out of ideas now. Please help me with it. All I want is that array getting encrypted after I pass it to the encrypt function (the size should remain the same)

Thanks in advance and regards,

Vineet

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