From 53619f9f40740ae8b256998574758aa191635db8 Mon Sep 17 00:00:00 2001 From: Hubert Kario Date: Mon, 1 Feb 2016 11:14:34 -0500 Subject: [PATCH] GH554: Improve pkeyutl doc Signed-off-by: Rich Salz Reviewed-by: Dr. Stephen Henson --- doc/apps/pkeyutl.pod | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/doc/apps/pkeyutl.pod b/doc/apps/pkeyutl.pod index a7b75e6c75..3c29b3a67c 100644 --- a/doc/apps/pkeyutl.pod +++ b/doc/apps/pkeyutl.pod @@ -137,6 +137,19 @@ Unless otherwise mentioned all algorithms support the B option which specifies the digest in use for sign, verify and verifyrecover operations. The value B should represent a digest name as used in the EVP_get_digestbyname() function for example B. +This value is used only for sanity-checking the lengths of data passed in to +the B and for creating the structures that make up the signature +(e.g. B 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 the input should be 20 bytes +long binary encoding of SHA-1 hash function output. =head1 RSA ALGORITHM -- 2.25.1