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GH554: Improve pkeyutl doc

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Signed-off-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Dr. Stephen Henson <steve@openssl.org>
(cherry picked from commit 53619f9f40740ae8b256998574758aa191635db8)
This commit is contained in:
Hubert Kario 2016-02-01 11:14:34 -05:00 committed by Rich Salz
parent a38a159bfc
commit 106dbca36c
1 changed files with 13 additions and 0 deletions
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doc/apps/pkeyutl.pod
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@ -137,6 +137,19 @@ 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