linux-kernel - Re: [RFC PATCH 4/4] crypto: Add EC-RDSA algorithm

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Date:   Mon, 7 Jan 2019 11:07:10 +0300
From:   Vitaly Chikunov <vt@...linux.org>
To:     Stephan Müller <smueller@...onox.de>
Cc:     David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 4/4] crypto: Add EC-RDSA algorithm

Stephan,

On Sun, Jan 06, 2019 at 07:11:50PM +0100, Stephan Müller wrote:
> Am Sonntag, 6. Januar 2019, 14:36:08 CET schrieb Vitaly Chikunov:
> 
> > Add Elliptic Curve Russian Digital Signature Algorithm (GOST R
> > 34.10-2012, RFC 7091, ISO/IEC 14888-3) is one of the Russian (and since
> > 2018 the CIS countries) cryptographic standard algorithms (called GOST
> > algorithms). Only signature verification is supported, with intent to be
> > used in the IMA.
> 
> Do you happen to have test vectors for the testmgr?

Yes, I will add this.

> > +/* Parse DER encoded subjectPublicKey. */
> > +static int ecrdsa_set_pub_key(struct crypto_akcipher *tfm, const void *ber,
> > +			      unsigned int len)
> > +{
> > +	struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
> > +	unsigned int ndigits;
> > +	const u8 *k = ber;
> > +	unsigned int offset;
> > +
> > +	/* First chance to zero ctx */
> > +	memset(ctx, 0, sizeof(*ctx));
> > +
> > +	if (len < 3 ||
> > +	    k[0] != 0x04 || /* OCTET STRING */
> > +	    (k[1] < 0x80 && len != k[1] + 2) ||
> > +	    (k[1] == 0x81 && len != k[2] + 3) ||
> > +	    k[1] > 0x81)
> > +		return -EBADMSG;
> > +	offset = (k[1] < 0x80)? 2 : 3;
> > +	k += offset;
> > +	len -= offset;
> 
> Why do you manually parse the ASN.1 structure instead of using the ASN.1 
> parser?

I am not sure this worth effort and will not be most degenerate use of
asn1_ber_decoder, since 1) I only need to parse one type in each case:
OCTET STRING string above code, and OIDs in below code; 2) this data is
said to be in DER format, which asn1_ber_decoder can not enforce. Surely
this will also produce more code and files.

> > +/* Parse DER encoded SubjectPublicKeyInfo.AlgorithmIdentifier.parameters.
> > */ +static int ecrdsa_set_params(struct crypto_akcipher *tfm, enum OID
> > algo, +			     const void *params, unsigned int paramlen)
> > +{
> > +	struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
> > +	const u8 *p = params;
> > +	int i;
> > +
> > +	if (algo == OID_gost2012PublicKey256) {
> > +		ctx->digest	= "streebog256";
> > +		ctx->digest_oid	= OID_gost2012Digest256;
> > +		ctx->digest_len	= 256 / 8;
> > +	} else if (algo == OID_gost2012PublicKey512) {
> > +		ctx->digest	= "streebog512";
> > +		ctx->digest_oid	= OID_gost2012Digest512;
> > +		ctx->digest_len	= 512 / 8;
> > +	} else
> > +		return -ENOPKG;
> > +	ctx->curve = NULL;
> > +	ctx->curve_oid = 0;
> > +	ctx->algo_oid = algo;
> > +
> > +	for (i = 0; i < paramlen; i += p[i + 1] + 2) {
> > +		const struct ecc_curve *curve;
> > +		enum OID oid;
> > +
> > +		if (paramlen - i < 2 ||
> > +		    p[i] != 0x06 || /* OBJECT IDENTIFIER */
> 
> Same here and in the following
> 
> > +		    p[i + 1] > paramlen - i - 2)
> > +			return -EBADMSG;
> > +		oid = look_up_OID(p + i + 2, p[i + 1]);

> > +MODULE_ALIAS_CRYPTO("ecrdsa");
> 
> I do not think you need that alias as the module name already will be named 
> this way. I guess you rather should add ecrdsa-generic as module alias.

Thanks!