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Revision a520723f29aac6598ff0d69e34f5e9b88213e511 authored by Matt Caswell on 14 October 2016, 12:07:00 UTC, committed by Matt Caswell on 28 October 2016, 08:43:41 UTC
Ensure we have length checks for all extensions
The previous commit inspired a review of all the length checks for the
extension adding code. This adds more robust checks and adds checks where
some were missing previously. The real solution for this is to use WPACKET
which is currently in master - but that cannot be applied to release
branches.

Reviewed-by: Rich Salz <rsalz@openssl.org>
1 parent 83a1d4b
Raw File
EVP_PKEY_derive.pod
=pod

=head1 NAME

EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key algorithm shared secret.

=head1 SYNOPSIS

 #include <openssl/evp.h>

 int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
 int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
 int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);

=head1 DESCRIPTION

The EVP_PKEY_derive_init() function initializes a public key algorithm
context using key B<pkey> for shared secret derivation.

The EVP_PKEY_derive_set_peer() function sets the peer key: this will normally
be a public key.

The EVP_PKEY_derive() derives a shared secret using B<ctx>.
If B<key> is B<NULL> then the maximum size of the output buffer is written to
the B<keylen> parameter. If B<key> is not B<NULL> then before the call the
B<keylen> parameter should contain the length of the B<key> buffer, if the call
is successful the shared secret is written to B<key> and the amount of data
written to B<keylen>.

=head1 NOTES

After the call to EVP_PKEY_derive_init() algorithm specific control
operations can be performed to set any appropriate parameters for the
operation.

The function EVP_PKEY_derive() can be called more than once on the same
context if several operations are performed using the same parameters.

=head1 RETURN VALUES

EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1 for success and 0
or a negative value for failure. In particular a return value of -2
indicates the operation is not supported by the public key algorithm.

=head1 EXAMPLE

Derive shared secret (for example DH or EC keys):

 #include <openssl/evp.h>
 #include <openssl/rsa.h>

 EVP_PKEY_CTX *ctx;
 unsigned char *skey;
 size_t skeylen;
 EVP_PKEY *pkey, *peerkey;
 /* NB: assumes pkey, peerkey have been already set up */

 ctx = EVP_PKEY_CTX_new(pkey);
 if (!ctx)
	/* Error occurred */
 if (EVP_PKEY_derive_init(ctx) <= 0)
	/* Error */
 if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
	/* Error */

 /* Determine buffer length */
 if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
	/* Error */

 skey = OPENSSL_malloc(skeylen);

 if (!skey)
	/* malloc failure */
 
 if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
	/* Error */

 /* Shared secret is skey bytes written to buffer skey */

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>,
L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>,
L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>,
L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>,
L<EVP_PKEY_verify_recover(3)|EVP_PKEY_verify_recover(3)>,

=head1 HISTORY

These functions were first added to OpenSSL 1.0.0.

=cut
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