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41 results

ecdh.c

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  • ecdh.c 4.07 KiB
    /* ECDH key-agreement protocol
     *
     * Copyright (c) 2016, Intel Corporation
     * Authors: Salvator Benedetto <salvatore.benedetto@intel.com>
     *
     * This program is free software; you can redistribute it and/or
     * modify it under the terms of the GNU General Public License
     * as published by the Free Software Foundation; either version
     * 2 of the License, or (at your option) any later version.
     */
    
    #include <linux/module.h>
    #include <crypto/internal/kpp.h>
    #include <crypto/kpp.h>
    #include <crypto/ecdh.h>
    #include <linux/scatterlist.h>
    #include "ecc.h"
    
    struct ecdh_ctx {
    	unsigned int curve_id;
    	unsigned int ndigits;
    	u64 private_key[ECC_MAX_DIGITS];
    };
    
    static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
    {
    	return kpp_tfm_ctx(tfm);
    }
    
    static unsigned int ecdh_supported_curve(unsigned int curve_id)
    {
    	switch (curve_id) {
    	case ECC_CURVE_NIST_P192: return 3;
    	case ECC_CURVE_NIST_P256: return 4;
    	default: return 0;
    	}
    }
    
    static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
    			   unsigned int len)
    {
    	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
    	struct ecdh params;
    	unsigned int ndigits;
    
    	if (crypto_ecdh_decode_key(buf, len, &params) < 0)
    		return -EINVAL;
    
    	ndigits = ecdh_supported_curve(params.curve_id);
    	if (!ndigits)
    		return -EINVAL;
    
    	ctx->curve_id = params.curve_id;
    	ctx->ndigits = ndigits;
    
    	if (!params.key || !params.key_size)
    		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
    				       ctx->private_key);
    
    	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
    			     (const u64 *)params.key, params.key_size) < 0)
    		return -EINVAL;
    
    	memcpy(ctx->private_key, params.key, params.key_size);
    
    	return 0;
    }
    
    static int ecdh_compute_value(struct kpp_request *req)
    {
    	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
    	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
    	u64 *public_key;
    	u64 *shared_secret = NULL;
    	void *buf;
    	size_t copied, nbytes, public_key_sz;
    	int ret = -ENOMEM;
    
    	nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
    	/* Public part is a point thus it has both coordinates */
    	public_key_sz = 2 * nbytes;
    
    	public_key = kmalloc(public_key_sz, GFP_KERNEL);
    	if (!public_key)
    		return -ENOMEM;
    
    	if (req->src) {
    		shared_secret = kmalloc(nbytes, GFP_KERNEL);
    		if (!shared_secret)
    			goto free_pubkey;
    
    		/* from here on it's invalid parameters */
    		ret = -EINVAL;
    
    		/* must have exactly two points to be on the curve */
    		if (public_key_sz != req->src_len)
    			goto free_all;
    
    		copied = sg_copy_to_buffer(req->src,
    					   sg_nents_for_len(req->src,
    							    public_key_sz),
    					   public_key, public_key_sz);
    		if (copied != public_key_sz)
    			goto free_all;
    
    		ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
    						ctx->private_key, public_key,
    						shared_secret);
    
    		buf = shared_secret;
    	} else {
    		ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
    				       ctx->private_key, public_key);
    		buf = public_key;
    		nbytes = public_key_sz;
    	}
    
    	if (ret < 0)
    		goto free_all;
    
    	/* might want less than we've got */
    	nbytes = min_t(size_t, nbytes, req->dst_len);
    	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
    								nbytes),
    				     buf, nbytes);
    	if (copied != nbytes)
    		ret = -EINVAL;
    
    	/* fall through */
    free_all:
    	kzfree(shared_secret);
    free_pubkey:
    	kfree(public_key);
    	return ret;
    }
    
    static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
    {
    	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
    
    	/* Public key is made of two coordinates, add one to the left shift */
    	return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
    }
    
    static struct kpp_alg ecdh = {
    	.set_secret = ecdh_set_secret,
    	.generate_public_key = ecdh_compute_value,
    	.compute_shared_secret = ecdh_compute_value,
    	.max_size = ecdh_max_size,
    	.base = {
    		.cra_name = "ecdh",
    		.cra_driver_name = "ecdh-generic",
    		.cra_priority = 100,
    		.cra_module = THIS_MODULE,
    		.cra_ctxsize = sizeof(struct ecdh_ctx),
    	},
    };
    
    static int ecdh_init(void)
    {
    	return crypto_register_kpp(&ecdh);
    }
    
    static void ecdh_exit(void)
    {
    	crypto_unregister_kpp(&ecdh);
    }
    
    module_init(ecdh_init);
    module_exit(ecdh_exit);
    MODULE_ALIAS_CRYPTO("ecdh");
    MODULE_LICENSE("GPL");
    MODULE_DESCRIPTION("ECDH generic algorithm");