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En/Decrypt Mismatch: Command-Line Tool vs. Crypt::OpenSSL::RSA

 
 
Jerry Krinock
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Posts: n/a
 
      08-14-2008
I posted this to openssl-users-at-openssl.org a couple days ago but no
one seems to know the answer.

I cannot get RSA-encrypted messages which I generate using
Crypt::OpenSSL::RSA to decrypt using the openssl command-line tool.
It may be something easy/stupid since I am a new openssl user.

Attempting to cut the problem in half, I then did another experiment
to see if they would generate the same signature. They don't. So I
conclude that the problem is in the ENcrypting. I gave both
encryptors (Crypt::OpenSSL::RSA and openssl command) the...

Same message
Same private key
Same padding (PKCS1)
Same digest (SHA1)
Both running on same Macintosh, presumably using the same
OpenSSL version 0.9.7l library in Mac OS X 10.5.4.

Here are my commands/code and results, starting with the command-line:

################################################## #############
# Create a private key
Jerrys-Mac-Mini: jk$ openssl genrsa -out Test248.private.pem
Generating RSA private key, 512 bit long modulus
..........++++++++++++
..............++++++++++++
e is 65537 (0x10001)

# Create signature of message "Bonehead" using the key in file
# Test248.private.pem, SHA1 digest and PKCS padding [1]:

Jerrys-Mac-Mini: jk$ echo -n "Bonehead" \
| openssl dgst -sha1 -binary\
| openssl rsautl -pkcs -sign -inkey Test248.private.pem -hexdump
0000 - 8a c6 56 19 97 f5 e7 16-20 30 f2 2f 0e af 7c 28
0010 - df 9d cd 5a 0e b0 11 c1-cc bb f2 3b 03 87 f0 96
0020 - 0d ce b4 55 dc 69 81 bc-30 40 75 9d 74 b8 b7 bd
0030 - 3b 15 a0 5d c2 db ab 9a-8d d3 f2 4b 77 e1 e9 a1
################################################## ############

Now I try to create the same signature using a perl script:

################################################## ############
#!/usr/local/bin/perl -w

use strict ;
use warnings ;

use Crypt::OpenSSL::Random ;
use Crypt::OpenSSL::RSA ;

# Read in the key file just created
my $private_key_string = "" ;
my $key_path = "/Users/jk/Documents/SheepSystems/Keys/
Test248.private.pem" ;
open (KEY_FILE, $key_path) ;
while (my $line = <KEY_FILE>) {
$private_key_string .= $line ;
}
close(KEY_FILE);

print "Read key from file:\n$private_key_string\n" ;

my $rsa_priv = Crypt::OpenSSL::RSA-
>new_private_key($private_key_string);


# Use same message, padding and digest as in the command-line test
my $msg = "Bonehead" ;
$rsa_priv->use_pkcs1_padding();
$rsa_priv->use_sha1_hash() ;

my $signature = $rsa_priv->sign($msg);
my $showHexSig = showHex($signature) ;
print "signature of 'Bonehead':\n$showHexSig\n" ;

# sub showHex is shown at the bottom of this message
################################################## ############

Running the above script, I get this:

################################################## ############
Read key from file:
-----BEGIN RSA PRIVATE KEY-----
MIIBOgIBAAJBALE2d5DpKbYxfIqv+6jYnW6DDvDyJFCdQt+s43 2GQsy8+ymL9DOR
mPcRQfk1jas1pqtsy+GGUlYd4R1kxbBZb4UCAwEAAQJANqtw83 ma7qQRoc9sucgp
uUAhSd/JqDz7tnllrQHQdcyLMRSCBxvZ/i72YVixRRTHb1GVZ79iJWBmzh8ATLvj
uQIhAOuYWu6Vkve+zQ4Cd5EGWpytY/Or/6ZXvQf3L9ELIB07AiEAwI+miVT8t22w
Ge1IX+Q3L7lK2uBm97Pkwix9Wf7K2j8CIFUrQtQ1ZmgBpgeGhM r8zQ0O8a9JYqYz
2bZjefnMV9O5AiEAqSrKLKYcKm1To0NhLNUKYoPPLkCsVPqWgr uhGDoOLfMCIE1E
kpJF13Dtq3KQOsaCoXbL4vo350vkBUrSovu45/6p
-----END RSA PRIVATE KEY-----

signature of 'Bonehead':
64 bytes:
78 b3 43 22 4b 4b 86 7f 47 25 00 f1 62 a2 66 70
e6 7e 82 f2 7a b6 cf ff ab dd f1 8a ff 0d cf a1
b5 3d 60 dc ac 9f 6f 0c 83 b9 51 c9 ac fa 7d 15
0b cc 97 cf 99 e5 6b ee 41 f0 d1 35 a1 a0 c1 09
################################################## ############

As you can see the two signatures are both 64 bytes long but do not
match.

What might I be missing?

Thanks very much,

Jerry Krinock

[1] The reason I used PKCS padding (-pkcs) is because if I change it
to -oaep in the command-line test, I get an error message:
RSA operation error
error:04066076:rsa routines:RSA_EAY_PRIVATE_ENCRYPT:unknown padding
type:rsa_eay.c:360:
which does not make sense because my version is:
Jerrys-Mac-Mini:Keys jk$ openssl
OpenSSL> version
OpenSSL 0.9.7l 28 Sep 2006
and "RSA_padding_add_PKCS1_OAEP() and RSA_padding_check_PKCS1_OAEP()
were added in OpenSSL 0.9.2b" according to documentation:
http://openssl.org/docs/crypto/RSA_p...1_type_1.html#

[2]
sub showHex {
my $data = shift ;
use bytes ;
my $len = length($data) ;
my $i ;
my $show = "" ;
for ($i=0; $i<$len; $i++) {
my $value = ord(substr($data, $i, 1)) ;
$show .= " " ;
$show .= sprintf("%02x", $value) ;
if ((($i+1) % 16) == 0) {
$show .= "\n" ;
}
}

return "$len bytes:\n$show" ;
}
 
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Jerry Krinock
Guest
Posts: n/a
 
      08-20-2008
Well, I got this working, although I there are several things that
don't seem to work they way they should. Short summary: Must use
perl function private_encrypt() instead of sign(), even though, to
generate the same signature, the command-line tool must use -sign.
Must use the SHA1 digest generated by command-line tool, since
$rsa_priv->use_sha1_hash() has no effect on private_encrypt().

I don't understand this well enough to say that these are bugs. More
comments are in the code in case anyone is interested.

Here are my revised commands/code and working results, starting with
the command-line:

################################################## #############
# Create a private key
jk$ openssl genrsa -out Test248.private.pem
Generating RSA private key, 512 bit long modulus
..........++++++++++++
..............++++++++++++
e is 65537 (0x10001)

# Create SHA1 digest of message "Bonehead".
# The, write digest to file for later use by perl script.
# Finally, sign the digest using the key in file Test248.private.pem
# and PKCS padding. Why PKCS? See note [1].
echo -n "Bonehead" > clearMsg.txt
openssl dgst -sha1 -binary -out msgDigest clearMsg.txt
cat msgDigest | openssl rsautl -pkcs -sign -inkey Test248.private.pem -
hexdump

0000 - 8a c6 56 19 97 f5 e7 16-20 30 f2 2f 0e af 7c 28
0010 - df 9d cd 5a 0e b0 11 c1-cc bb f2 3b 03 87 f0 96
0020 - 0d ce b4 55 dc 69 81 bc-30 40 75 9d 74 b8 b7 bd
0030 - 3b 15 a0 5d c2 db ab 9a-8d d3 f2 4b 77 e1 e9 a1
################################################## ############

Now create the same signature using a Crypt::OpenSSL in Perl:

################################################## ############
#!/usr/local/bin/perl -w

use strict ;
use warnings ;

use Crypt::OpenSSL::Random ;
use Crypt::OpenSSL::RSA ;

# Read in key from file
my $private_key_string = "" ;
my $key_path = "/Users/jk/Documents/SheepSystems/Keys/
Test248.private.pem" ;
open (KEY_FILE, $key_path) ;
while (my $line = <KEY_FILE>) {
$private_key_string .= $line ;
}
close(KEY_FILE);
print "Read key from file:\n$private_key_string\n" ;

my $rsa_priv = Crypt::OpenSSL::RSA-
>new_private_key($private_key_string);


$rsa_priv->use_pkcs1_padding() ;
=com
Padding is a big mystery.
The above affects encrypting with the private key
but does not affect signature generation. As a matter of
fact, it is necessary when using the private_encrypt()
method. Without the above, private_encrypt() will fail
with error. I believe the problem is that OpenSSL does not
support oaep padding for signing, which is what you're
doing when you encrypt with the private key, despite doc to
the contrary. See note [2].
=cut


# $rsa_priv->use_sha1_hash() ;
# The above has no effect on the output of the
# private_encrypt() method. So, I don't use it.

my $output ;
my $outputHex ;


my $msgDigest ;
my $msgDigest_path = "/Users/jk/Documents/SheepSystems/Keys/
msgDigest" ;
open (MSG_DIGEST_FH, $msgDigest_path) ;
# SHA1 Digest is 20 bytes...
read MSG_DIGEST_FH, $msgDigest, 20 ;
close(MSG_DIGEST_FH) ;
$output = $rsa_priv->private_encrypt($msgDigest);
# If you use sign() instead of private_encrypt()
# above you get a different output. This does not make sense
# to me because I thought that signing was the same as
# encrypting with the private key.
$outputHex = showHex($output) ;
print "privately encrypted msgDigest:\n$outputHex\n" ;

# sub showHex is shown at the bottom of this message
################################################## ############

Running the above script, I get this:

################################################## ############
Read key from file:
-----BEGIN RSA PRIVATE KEY-----
MIIBOgIBAAJBALE2d5DpKbYxfIqv+6jYnW6DDvDyJFCdQt+s43 2GQsy8+ymL9DOR
mPcRQfk1jas1pqtsy+GGUlYd4R1kxbBZb4UCAwEAAQJANqtw83 ma7qQRoc9sucgp
uUAhSd/JqDz7tnllrQHQdcyLMRSCBxvZ/i72YVixRRTHb1GVZ79iJWBmzh8ATLvj
uQIhAOuYWu6Vkve+zQ4Cd5EGWpytY/Or/6ZXvQf3L9ELIB07AiEAwI+miVT8t22w
Ge1IX+Q3L7lK2uBm97Pkwix9Wf7K2j8CIFUrQtQ1ZmgBpgeGhM r8zQ0O8a9JYqYz
2bZjefnMV9O5AiEAqSrKLKYcKm1To0NhLNUKYoPPLkCsVPqWgr uhGDoOLfMCIE1E
kpJF13Dtq3KQOsaCoXbL4vo350vkBUrSovu45/6p
-----END RSA PRIVATE KEY-----

privately encrypted msgDigest:
64 bytes:
8a c6 56 19 97 f5 e7 16 20 30 f2 2f 0e af 7c 28
df 9d cd 5a 0e b0 11 c1 cc bb f2 3b 03 87 f0 96
0d ce b4 55 dc 69 81 bc 30 40 75 9d 74 b8 b7 bd
3b 15 a0 5d c2 db ab 9a 8d d3 f2 4b 77 e1 e9 a1

################################################## ############

which matches the output from the command-line openssl.

Thanks for reading. If anyone can explain some of the anomalies
noted, let us know.

Jerry


[1] The reason I used PKCS padding (-pkcs) is because if I change it
to -oaep in the command-line test, I get an error message:
RSA operation error
error:04066076:rsa routines:RSA_EAY_PRIVATE_ENCRYPT:unknown padding
type:rsa_eay.c:360:
which does not make sense because my version is:

Jerrys-Mac-Mini:Keys jk$ openssl
OpenSSL> version
OpenSSL 0.9.7l 28 Sep 2006

and "RSA_padding_add_PKCS1_OAEP() and RSA_padding_check_PKCS1_OAEP()
were added in OpenSSL 0.9.2b" according to documentation:
http://openssl.org/docs/crypto/RSA_p...1_type_1.html#

[2]
sub showHex {
my $data = shift ;
use bytes ;
my $len = length($data) ;
my $i ;
my $show = "" ;
for ($i=0; $i<$len; $i++) {
my $value = ord(substr($data, $i, 1)) ;
$show .= " " ;
$show .= sprintf("%02x", $value) ;
if ((($i+1) % 16) == 0) {
$show .= "\n" ;
}
}

return "$len bytes:\n$show" ;
}
 
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