Selon Kyle Hamilton <aerow...@gmail.com>: > On Thu, May 21, 2009 at 11:55 PM, loody <milo...@gmail.com> wrote: > > Hi: > > > > thanks for your help. > > By your explanation, in der form, the leading 00 seems like a padding byte. > > ( Is there spec which says it must put 00 here?) > > from my example, the number af:4f:8a:97:....14:f7 is negative, since > > the high bit, 0xaf, is set. > > appreciate your kind help, > > miloody > > Yes, there is a specification which states that you must put 00 there. > It's called the "Distinguished Encoding Rules" of the "Abstract > Syntax Notation One" (ASN.1). The DER can be found in the ITU > document number X.690; the ASN.1 can be found in ITU document number > X.680.
This is specified in BER, not in DER: X.690 8.3. 8.3 ENCODING OF AN INTEGER VALUE 8.3.1 The encoding of an integer value shall be primitive. The contents octets shall consist of one or more octets. 8.3.2 If the contents octets of an integer value encoding consist of more than one octet, then the bits of the first octet and bit 8 of the second octet a) shall not all be ones; and b) shall not all be zero. NOTE These rules ensure that an integer value is always encoded in the smallest possible number of octets. 8.3.3The contents octets shall be a twos complement binary number equal to the integer value, and consisting of bits 8 to 1 of the first octet, followed by bits 8 to 1 of the second octet, followed by bits 8 to 1 of each octet in turn up to and including the last octet of the contents octets. NOTE The value of a twos complement binary number is derived by numbering the bits in the contents octets, starting with bit 1 of the last octet as bit zero and ending the numbering with bit 8 of the first octet. Each bit is assigned a numerical value of 2N, where N is its position in the above numbering sequence. The value of the twos complement binary number is obtained by summing the numerical values assigned to each bit for those bits which are set to one, excluding bit 8 of the first octet, and then reducing this value by the numerical value assigned to bit 8 of the first octet if that bit is set to one. > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org > User Support Mailing List openssl-users@openssl.org > Automated List Manager majord...@openssl.org > :§I"Ï®ÞrØm¶ÿà (¥éì²Z+K +©¦í1¨¥x Ëh¥éì²[¬z»(¥éì²Z+ ¢fyÒâ²Ó¨ ®f£¢·h)z{,à
