=pod

=head1 NAME

pkeyutl - public key algorithm utility

=head1 SYNOPSIS

B<openssl> B<pkeyutl>
[B<-help>]
[B<-in file>]
[B<-out file>]
[B<-sigfile file>]
[B<-inkey file>]
[B<-keyform PEM|DER|ENGINE>]
[B<-passin arg>]
[B<-peerkey file>]
[B<-peerform PEM|DER|ENGINE>]
[B<-pubin>]
[B<-certin>]
[B<-rev>]
[B<-sign>]
[B<-verify>]
[B<-verifyrecover>]
[B<-encrypt>]
[B<-decrypt>]
[B<-derive>]
[B<-kdf algorithm>]
[B<-kdflen length>]
[B<-pkeyopt opt:value>]
[B<-hexdump>]
[B<-asn1parse>]
[B<-engine id>]
[B<-engine_impl>]

=head1 DESCRIPTION

The B<pkeyutl> command can be used to perform public key operations using
any supported algorithm.

=head1 COMMAND OPTIONS

=over 4

=item B<-help>

Print out a usage message.

=item B<-in filename>

This specifies the input filename to read data from or standard input
if this option is not specified.

=item B<-out filename>

specifies the output filename to write to or standard output by
default.

=item B<-sigfile file>

Signature file, required for B<verify> operations only

=item B<-inkey file>

the input key file, by default it should be a private key.

=item B<-keyform PEM|DER|ENGINE>

the key format PEM, DER or ENGINE. Default is PEM.

=item B<-passin arg>

the input key password source. For more information about the format of B<arg>
see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.


=item B<-peerkey file>

the peer key file, used by key derivation (agreement) operations.

=item B<-peerform PEM|DER|ENGINE>

the peer key format PEM, DER or ENGINE. Default is PEM.

=item B<-pubin>

the input file is a public key. 

=item B<-certin>

the input is a certificate containing a public key. 

=item B<-rev>

reverse the order of the input buffer. This is useful for some libraries
(such as CryptoAPI) which represent the buffer in little endian format.

=item B<-sign>

sign the input data and output the signed result. This requires
a private key.

=item B<-verify>

verify the input data against the signature file and indicate if the
verification succeeded or failed.

=item B<-verifyrecover>

verify the input data and output the recovered data.

=item B<-encrypt>

encrypt the input data using a public key.

=item B<-decrypt>

decrypt the input data using a private key.

=item B<-derive>

derive a shared secret using the peer key.

=item B<-kdf algorithm>

Use key derivation function B<algorithm>.  The supported algorithms are
at present B<TLS1-PRF> and B<HKDF>.
Note: additional paramers and the KDF output length will normally have to be
set for this to work.  See L<EVP_PKEY_HKDF(3)> and L<EVP_PKEY_TLS1_PRF(3)>
for the supported string parameters of each algorithm.

=item B<-kdflen length>

Set the output length for KDF.

=item B<-pkeyopt opt:value>

Public key options specified as opt:value. See NOTES below for more details.

=item B<-hexdump>

hex dump the output data.

=item B<-asn1parse>

asn1parse the output data, this is useful when combined with the
B<-verifyrecover> option when an ASN1 structure is signed.

=item B<-engine id>

specifying an engine (by its unique B<id> string) will cause B<pkeyutl>
to attempt to obtain a functional reference to the specified engine,
thus initialising it if needed. The engine will then be set as the default
for all available algorithms.

=item B<-engine_impl>

When used with the B<-engine> option, it specifies to also use
engine B<id> for crypto operations.

=back

=head1 NOTES

The operations and options supported vary according to the key algorithm
and its implementation. The OpenSSL operations and options are indicated below.

Unless otherwise mentioned all algorithms support the B<digest:alg> option
which specifies the digest in use for sign, verify and verifyrecover operations.
The value B<alg> should represent a digest name as used in the
EVP_get_digestbyname() function for example B<sha1>.
This value is used only for sanity-checking the lengths of data passed in to
the B<pkeyutl> and for creating the structures that make up the signature
(e.g. B<DigestInfo> in RSASSA PKCS#1 v1.5 signatures).
In case of RSA, ECDSA and DSA signatures, this utility
will not perform hashing on input data but rather use the data directly as
input of signature algorithm. Depending on key type, signature type and mode
of padding, the maximum acceptable lengths of input data differ. In general,
with RSA the signed data can't be longer than the key modulus, in case of ECDSA
and DSA the data shouldn't be longer than field size, otherwise it will be
silently truncated to field size.

In other words, if the value of digest is B<sha1> the input should be 20 bytes
long binary encoding of SHA-1 hash function output.

=head1 RSA ALGORITHM

The RSA algorithm generally supports the encrypt, decrypt, sign,
verify and verifyrecover operations. However, some padding modes
support only a subset of these operations. The following additional
B<pkeyopt> values are supported:

=over 4

=item B<rsa_padding_mode:mode>

This sets the RSA padding mode. Acceptable values for B<mode> are B<pkcs1> for
PKCS#1 padding, B<sslv23> for SSLv23 padding, B<none> for no padding, B<oaep>
for B<OAEP> mode, B<x931> for X9.31 mode and B<pss> for PSS.

In PKCS#1 padding if the message digest is not set then the supplied data is 
signed or verified directly instead of using a B<DigestInfo> structure. If a
digest is set then the a B<DigestInfo> structure is used and its the length
must correspond to the digest type.

For B<oaep> mode only encryption and decryption is supported.

For B<x931> if the digest type is set it is used to format the block data
otherwise the first byte is used to specify the X9.31 digest ID. Sign,
verify and verifyrecover are can be performed in this mode.

For B<pss> mode only sign and verify are supported and the digest type must be
specified.

=item B<rsa_pss_saltlen:len>

For B<pss> mode only this option specifies the salt length. Two special values
are supported: -1 sets the salt length to the digest length. When signing -2
sets the salt length to the maximum permissible value. When verifying -2 causes
the salt length to be automatically determined based on the B<PSS> block
structure.

=back

=head1 DSA ALGORITHM

The DSA algorithm supports signing and verification operations only. Currently
there are no additional options other than B<digest>. Only the SHA1
digest can be used and this digest is assumed by default.

=head1 DH ALGORITHM

The DH algorithm only supports the derivation operation and no additional
options.

=head1 EC ALGORITHM

The EC algorithm supports sign, verify and derive operations. The sign and
verify operations use ECDSA and derive uses ECDH. Currently there are no
additional options other than B<digest>. Only the SHA1 digest can be used and
this digest is assumed by default.

=head1 EXAMPLES

Sign some data using a private key:

 openssl pkeyutl -sign -in file -inkey key.pem -out sig

Recover the signed data (e.g. if an RSA key is used):

 openssl pkeyutl -verifyrecover -in sig -inkey key.pem

Verify the signature (e.g. a DSA key):

 openssl pkeyutl -verify -in file -sigfile sig -inkey key.pem

Sign data using a message digest value (this is currently only valid for RSA):

 openssl pkeyutl -sign -in file -inkey key.pem -out sig -pkeyopt digest:sha256

Derive a shared secret value:

 openssl pkeyutl -derive -inkey key.pem -peerkey pubkey.pem -out secret

Hexdump 48 bytes of TLS1 PRF using digest B<SHA256> and shared secret and
seed consisting of the single byte 0xFF:

 openssl pkeyutl -kdf TLS1-PRF -kdflen 48 -pkeyopt md:SHA256 \
    -pkeyopt hexsecret:ff -pkeyopt hexseed:ff -hexdump

=head1 SEE ALSO

L<genpkey(1)>, L<pkey(1)>, L<rsautl(1)>
L<dgst(1)>, L<rsa(1)>, L<genrsa(1)>,
L<EVP_PKEY_HKDF(3)>, L<EVP_PKEY_TLS1_PRF(3)>
