Dear List,
I have found a BUG in the function
" RSA_padding_check_PKCS1_type_1 "
The bug is reproducible in OpenSSL Versions 1.0.1e , 1.0.1p , 1.0.1k and also
in 1.0.2d (these are the versions I've tried) . After Inspecting the source
code the bug can still be found in the actual development branch.
Description:
When a correctly formatted PKCS1 Type 1 data string is given to the method "
RSA_padding_check_PKCS1_type_1 " it always results in:
OpenSSLError: Code:67567722 in file:rsa_pk1.c line:102.
OpenSSLError: Error Message: error:0407006A:rsa
routines:RSA_padding_check_PKCS1_type_1:block type is not 01
Even when the message was originally padded by the corresponding OpenSSL
Padding Function " RSA_padding_add_PKCS1_type_1" the same error occurs.
Cause:
In the File crypto/rsa/rsa_pk1.c
Following check is made to determine the Block type of the padding string
const unsigned char *p;
p=from;
if ((num != (flen+1)) || (*(p++) != 01))
the pointer p is incremented after the check therefore p is always the first
octet of the padded string. In the Case of PKCS1 type 1 padding always p=0,
hence the error.
Notes:
Changing the check to
if ((num != (flen+1)) || (*(++p) != 01))
results also in a failure since the next check of p expects p to be "0xff" .
Fix:
Adding an increment before the check:
const unsigned char *p;
p=from;
p++; //NEW
if ((num != (flen+1)) || (*(p++) != 01))
fixes the problem.
Question:
What does the the first part of the Check , check exactly ?
Ie:
num != (flen+1)
num being rsa_size and flen the length of the buffer where the message is
stored.
Thanks
Dipl.-Inf T. Jonas Özgan
Cyber Analysis & Defense Department
Fraunhofer Institute for Communication, Information Processing and Ergonomics
(FKIE)
Fraunhoferstr. 20 | 53343 Wachtberg | Germany
Tel: +49 228 9435-513 | Fax +49 228 9435-685
http://www.fkie.fraunhofer.de
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