Hello,
It looks like the functions asn1_encode_integer() and
sc_asn1_decode_integer() from src/libopensc/asn1.c are not correct.
For example the integer 128 is encoded 0x80 but should be encoded 0x00
0x80. 0x80 is the encoding of -128
-128 is encoded FF FF FF 80 but I don't know if that is a valid coding.
I am not expert in ASN.1 so am not sure it is a bug.
I found ASN.1 encoding examples in [1]:
##
## INTEGER (tests 13 - 21)
##
my %INTEGER = (
pack("C*", 0x02, 0x02, 0x00, 0x80), 128,
pack("C*", 0x02, 0x01, 0x80), -128,
pack("C*", 0x02, 0x02, 0xff, 0x01), -255,
pack("C*", 0x02, 0x01, 0x00), 0,
pack("C*", 0x02, 0x03, 0x66, 0x77, 0x99), 0x667799,
pack("C*", 0x02, 0x02, 0xFE, 0x37), -457,
pack("C*", 0x02, 0x04, 0x40, 0x00, 0x00, 0x00), 2**30,
pack("C*", 0x02, 0x04, 0xC0, 0x00, 0x00, 0x00), -2**30,
);
I propose the attached patch for asn1_encode_integer().
sc_asn1_decode_integer() should also be patched.
Do we have ASN.1 experts on this list?
bye
[1] http://search.cpan.org/src/GBARR/Convert-ASN1-0.21/t/00prim.t
--
Dr. Ludovic Rousseau
Index: src/libopensc/asn1.c
===================================================================
--- src/libopensc/asn1.c (révision 3386)
+++ src/libopensc/asn1.c (copie de travail)
@@ -546,7 +546,7 @@ static int asn1_encode_integer(int in, u
int i = sizeof(in) * 8, skip = 1;
u8 *p, b;
- *obj = p = (u8 *) malloc(sizeof(in));
+ *obj = p = (u8 *) malloc(sizeof(in)+1);
if (*obj == NULL)
return SC_ERROR_OUT_OF_MEMORY;
do {
@@ -554,7 +554,12 @@ static int asn1_encode_integer(int in, u
b = in >> i;
if (b == 0 && skip)
continue;
- skip = 0;
+ if (skip) {
+ skip = 0;
+ /* prepend 00 if MSb is 1 and integer positive */
+ if ((b & 0x80) != 0 && in > 0)
+ *p++ = 0;
+ }
*p++ = b;
} while (i > 0);
*objsize = p - *obj;
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