Cryptography Reference
In-Depth Information
ECashScheme - Preliminary Description
Suppose that Bob wants to withdraw $100 from his account at the bank
and use it to spend at a vendor to purchase merchandise electronically. The
following protocol is enacted.
ECashWithdrawal
1. Bob generates 100 sets of identitystrings, and uses a secret-splitting protocol
to split each one into two pieces.
2. Bob prepares 100 moneyorders for $100 each, uses a blinding protocol, and
sends the blinded orders to the bank (including his split-identitystrings).
3. The bank, after verification of validityusing a cut-and-choose protocol,
encrypts the identification number of one of the 100 blank coins with its
signature to form a valid moneyorder, debits Bob's account, and sends
the moneyorder to Bob. If verification fails the bank reports to the
authorities.
4. Bob unblinds the signed coin in the moneyorder, which he can now use to
spend with a vendor via the moneyorder.
ECashSpending
1. Bob sends the moneyorder to the vendor, who verifies the bank's signature.
2. The vendor uses the secret-splitting generated byBob in step 1 of the
withdrawal stage and sends the moneyorder to the bank for verification.
3. The bank checks the coin against its used coin database. If it is not there,
the bank credits the vendor's account with $100 and the vendor sends the
goods to Bob, and the transaction is complete. If the coin
is
there, the
bank executes step 4.
4. The bank rejects the moneyorder and uses the identitystrings to identify
Bob.
Now we get the details of how the above is accomplished.
ECash
TM
Scheme — Full Description
ECashWithdrawal Details
100
1. Bob generates 100 sets of unique digital data strings
S
j
=
{
I
j
k
}
k
=1
for
1
100 such that
each
I
j
k
uniquelyidentifies him. He then engages
in a secret-splitting protocol so that, for each
j
=1
,...,
100, the digital
data string is split into two pieces
I
j
k
=
≤
j
≤
{
L
j
k
,R
j
k
}
with
I
⊕
I
r
identifying
100
Bob if and onlyif
=
r
, where
, r
∈{
j
k
}
k
=1
.
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