cryptography - Does DESKey preserve invalid parity bits? -


according des specification, last bit of each byte of secret key used error detection (each byte should have odd parity). hence effective key length 56 bits, not 64 bits.

however, in many use cases these parity bits not checked. used different purpose: mifare desfire cards store key version in bits, example, though original error correction purpose gets lost.

how java card implementations handle these bits? let have @ code:

deskey deskey = ... //a single des key instance byte[] inputkey = new byte[8]; inputkey[7] = (byte) 0x03; //explicitly invalid parity bit in last byte deskey.setkey(inputkey, (short) 0); byte[] outputkey = new byte[8]; deskey.getkey(outputkey, (short) 0);

is guaranteed inputkey , outputkey arrays contain same data in end, invalid parity bits in inputkey? performed several experiments few card types , preserve data put in parity bits, didn't find mention in java card specification behaviour guaranteed.

this piece of information important me; otherwise have store "invalid parity bits" separated key instance.

if not in specifications not guaranteed. it's simple; there isn't separate specification card implementers says otherwise (and if there was, might change without touching original definition).

operations on keys can tricky regard attacks. there lot said keeping key data intact , not iterate on key bits using generic cpu. also, might tricky when other operations performed on key data such calculating key check value using hash function or using same key input mac (symmetric signature).

it's of course possible perform parity operation on key bits using own code. can compare result test vectors or keys generated using java secretkeyfactory. however, since parity bits don't used in key calculations, needed if want export key out of device. again, note performing additional operations on key data dangerous , may break kinds of security tests/proofs/certifications.

note java card implementations (or rather, hardware of underlying chip) perform checksums on persistent (eeprom/flash) memory anyway. it's keys protected java card implementation (or 1 of underlying layers). regards protection against unforeseen alterations of data: wouldn't worry overly much. don't need des parity bits that.

ok, felt doing bit fiddling, here's java card code set parity (i'll let loop , inlining , stuff, if don't mind). these calculations should (near) constant time.

/**  * method takes byte value <code>b</code> , sets or unsets least significant bit  * of value in such way parity of <code>b</code> odd.  * method returns either <code>b</code> or <code>b ^ 1</code>.  *   * @param b byte value  * @return <code>b</code> des parity  */ public static byte makedesparity(final byte b) {     byte x = b;     // trick calculate odd parity in lsb of x     x ^= x >>> 4;     x ^= x >>> 2;     x ^= x >>> 1;     // want parity in lsb: ~x     // least significant bit: ~x & 1     // xor b: ~x & 1 ^ b     return (byte) (~x & 1 ^ b); }  /**  * method takes byte value <code>b</code> , returns true if , if  * byte has odd parity.  *   * @param b byte value  * @return true if <code>b</code> has des parity  */ public static boolean hasdesparity(byte b) {     // trick calculate odd parity in lsb of b     b ^= b >>> 4;     b ^= b >>> 2;     b ^= b >>> 1;     // check if last bit has indeed been set     return (b & 1) != 0; }

Comments

Post a Comment

Popular posts from this blog

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

sql server - Why does Linq-to-SQL add unnecessary COUNT()? -

here tables: create table customer ( cid int primary key, name varchar(32) ) create table ord ( oid int primary key, cid int foreign key references customer, address varchar(20) ) here's linq-to-sql statement: var aaa = c in db.customer select new { c, o = c.ord.tolist() }; and here's inexplicable query generated linq-to-sql: select [t0].[cid] [cid], [t0].[name] [name], [t1].[oid] [oid], [t1].[cid] [cid2], [t1].[address] [address], (select count(*) [dbo].[ord] [t2] [t2].[cid] = [t0].[cid]) [value] [dbo].[customer] [t0] left outer join [dbo].[ord] [t1] on [t1].[cid] = [t0].[cid] order [t0].[cid], [t1].[oid] i want understand how rid of count(*) part. it's entirely uncalled for! linq needs count(*) in order determine number of entries returned o = c.ord.tolist() .
Read more