EldoS | Feel safer!

Software components for data protection, secure storage and transfer

ECDSA Questions

Also by EldoS: CallbackFilter
A component to monitor and control disk activity, track file and directory operations (create, read, write, rename etc.), alter file data, encrypt files, create virtual files.
Posted: 11/09/2009 12:28:11
by Denis Sletkov (Standard support level)
Joined: 11/27/2007
Posts: 14

I sign detached using ECDSA and have some questions about it:
1. When i sign with SignDetached with zero size when say about 44 bytes (for OID_EC_SECP112R1) but real size vary between 34 or 36. Is this size fixed or float and in which range it can vary?
2. When i see signature i find that first four bytes looks
#48#33#2#15 - if 35 byte size
#48#32#2#14 - if 34 byte size
#48#34#2#15 - if 36 byte size
is this some type of signature header (if so) where i can this inforimation.
3. Does sbb support less than 112 bit keys to produce less signature.
Thank you in advance.
Posted: 11/09/2009 13:18:11
by Mykola Olshevsky (Basic support level)
Joined: 07/07/2005
Posts: 450

Hi, thank you for interest in our product.
1, 2. ECDSA signature is of ASN.1 SEQUENCE type, which contains two ASN.1 integers, and, regarding to ASN.1 notation, to those integers is prepended additional zero byte if their higher bit is 1. So, that's why you can receive from 34 to 36 bytes of output.

3. 112 bits field size is the smallest one defined in standards, so SBB supports predefined curves only of this size and larger. However, you can use custom fields of smaller size, but it is only if you know what are you doing, and only at your own risk :)



Topic viewed 1217 times

Number of guests: 1, registered members: 0, in total hidden: 0


Back to top

As of July 15, 2016 EldoS Corporation will operate as a division of /n software inc. For more information, please read the announcement.

Got it!