Partial hashing
843851Aug 14 2009 — edited Aug 14 2009Hello
I got my hands on a card that in order to perform a Digital Signature the data has to be passed has a Partial Hash. It only supports this kind of hashing method
Well, putting it simple I do not know how to perform this.
The APDU format for the PSO where the data is passed is the following:
Cla: 0x00
INS: 0x2A - For PSO
P1: 90 - For hashing
P2: A0 - For hash calculation of the data
Data: CRT DST with the following TLV structure
0x90, 0x1C, Intermediate hash value and number of bit already hashed (coded over 8 bytes = MSB...LSB);
0x80, Var (<= 0x40); Last block, to be hashed by the card
I also do not understand how to configure this DST.
In the DST, the field with tag 0x90 is with length 28 bytes (1C). This means that is the regular 20 bytes from an hash plus 8 other bytes? What other bytes?
And also in the DST but for the tag 0x80 what is the last block?
The Google searches are not helping much, so, any tips regarding partial hashing?
Ty
Cad