[taler-donau] branch master updated: edits

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grothoff pushed a commit to branch master
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The following commit(s) were added to refs/heads/master by this push:
     new 8e2c7d0  edits
8e2c7d0 is described below

commit 8e2c7d055926e7929b93edc80a9a1f5f77b2f853
Author: Christian Grothoff <grothoff@gnunet.org>
AuthorDate: Tue Oct 3 15:12:32 2023 +0200

    edits
---
 doc/flows/main.tex | 86 +++++++++++++++++++++++++++++-------------------------
 1 file changed, 47 insertions(+), 39 deletions(-)

diff --git a/doc/flows/main.tex b/doc/flows/main.tex
index 3d2e322..fb5a769 100644
--- a/doc/flows/main.tex
+++ b/doc/flows/main.tex
@@ -21,24 +21,30 @@
 
 \section{Definitions}
 \begin{itemize}
-  \item $DU :=$ \textbf{donation unit} = Smallest structure representing a 
donation confirmation unit, e.g. receipt for CHF1, CHF2. Equivalent in Taler is 
"coin".
-  \item $BDU :=$ blinded DU
-  \item $DR :=$ \textbf{donation receipt} = collection of DUs for one donation
-  \item $BDR :=$ collection of BDUs
-  \item $DS_{year} :=$ \textbf{donation statement} = sum of DRs for one 
specific year and specific donor
-  \item $b :=$ blinding factor
-  \item $H :=$ cryptographic hash function
+\item $DU :=$ \textbf{donation unit} = Smallest structure representing a 
donation confirmation unit, e.g. receipt for CHF1, CHF2. Equivalent in Taler is 
"denomination".
+  \item $UDID := $ unique identifier of a donor by tax ID, made unique per 
donation to obtain unique $DR$s per donation
+  \item $BDID :=$ blinded $UDID$, blinded for privacy of the donor 
   \item $BS :=$ BDU blinded signature made with a donation unit secret key 
(from DONAU)
   \item $S :=$ unblinded BS
-  \item $DUi, Si, DRi...$ := number entities if there are more than one eg. 
DU1,DU2...
+  \item $DR :=$ \textbf{donation receipt} = $UDID$ with $S$ signature of DONAU 
affirming donation over the respectiv amount as given by the DU associated with 
the signature
+  \item $DRs :=$ collection of $DR$s
+  \item $DS_{year} :=$ \textbf{donation statement} = confirmation over the 
total amount of DRs produced for a specific year and specific donor (DID)
+  \item $b :=$ blinding factor
+  \item $H :=$ cryptographic hash function
+  \item $DUi, Si, DRi, \ldots$ := number entities if there are more than one 
e.g. $DU1$, $DU2$ ...
   \item $BS_{kj}$ or $S_{kj} \Rightarrow kj$ := specific DONAU public key used 
to attribute a specific value to a DU, e.g. k1 gives the DU a value of 1, k2 a 
value of 2...
 \end{itemize}
 
-\subsection{Donation Unit (DU)}
-The NONCE is used to uniquely distinguish DU of the same value ("create a 
fresh DU"). Otherwise the DONAU would refuse DUs containing donations of equal 
amount to the same charity, since this would be seen as "double spending". To 
simplify the thought process, the NONCE can be thought of as a "DU ID".
+\subsection{Unique Donor ID (UDID)}
+
+The NONCE is used to uniquely distinguish donor IDs of the same value
+("create a fresh donor ID").  Otherwise the DONAU would refuse DUs
+containing donations of equal amount to the same charity, since this
+would be seen as "double spending" (or rather, double claiming of
+tax deduction for the same donation). 
 
 \begin{align}
-  DU := \langle H(TAXID, SALT), NONCE \rangle
+  UDID := \langle H(TAXID, SALT), NONCE \rangle
 \end{align}
 
 \section{Overview}
@@ -46,70 +52,73 @@ The NONCE is used to uniquely distinguish DU of the same 
value ("create a fresh
 
 \subsection{Step 0: Initial setup}
 \begin{enumerate}
-  \item key generation for blind signatures and statement signing. Distribute 
the keys.
-  \item The charity generates their own key pair.
+  \item Key generation for blind signatures and statement signing by the 
DONAU. Distribution of the keys to charities, donors and tax authorities 
(possibly on-demand via REST API). Let $ki$ be the private key for $i$ DU and 
$Pi$ be the corresponding public key. 
+  \item The charity generates their own key pair (charity pub/priv).
   \item The DONAU administrator registers the public key of the charity and 
sets the yearly donation limit for the charities.
 \end{enumerate}
 
 \subsection{Attest donation}
 \subsubsection{Step 1: Donor donates to charity}
 \begin{enumerate}
-  \item The donor downloads the DU public keys for the corresponding year from 
the DONAU.
+  \item The donor downloads the DU public keys $P1, P4$ for the corresponding 
year from the DONAU.
 
-  \item To donate 5 Euros the donor has to generate 2 DUs (a 1 Euro and 4 Euro 
DU). The donor generates DUs $DU1$ and $DU2$ which include a salted hash of the 
tax number (here TAXID) and a NONCE. % not DUs, DRs!
+  \item To donate 5 Euros the donor has to generate 2 UDIDs (for 1 Euro and 4 
Euro DU).
+    The donor generates UDIDs $U1$ and $U2$ which include a salted hash of the 
tax number
+    (here TAXID) and a NONCE.
 
   \begin{align}
-    DU1 = \langle H(TAXID, SALT), NONCE_1 \rangle \\ % These are (prototypes) 
for DRs! DUs are the 1 EUR and 4 EUR!
-    DU2 = \langle H(TAXID, SALT), NONCE_2 \rangle % Maybe call these UDIDs? 
(Unique Donor Ids)
+    U1 = \langle H(TAXID, SALT), NONCE_1 \rangle \\ % These are (prototypes) 
for DRs! DUs are the 1 EUR and 4 EUR!
+    U2 = \langle H(TAXID, SALT), NONCE_2 \rangle % Maybe call these UDIDs? 
(Unique Donor Ids)
   \end{align}
 
   \item The donor blinds the DUs using two different blinding factors $b_1, 
b_2$.
   \begin{align}
-    BDU1 = blind(b_1,DU1) \\ % BDR!
-    BDU2 = blind(b_2,DU2) % This is RSA-style blinding, in the abstract just 
use "blind(b_1,UDID)"
+    BU1 = \langle blind(b_1,U1, P1), H(P1) \rangle \\ % BDR!
+    BU2 = \langle blind(b_2,U2, P4), H(P4) \rangle
   \end{align}
 
-\item The donor sends the blinded DUs (BDR) $BDU1$ and $BDU2$ as well as the 
payment of 5 Euros.
+\item The donor sends the blinded UDIDs (BDIDs) $BU1$ and $BU2$ as well as the 
payment of 5 Euros.
 
 \end{enumerate}
 
-\subsubsection{Charity sends signed DUs to DONAU}
+\subsubsection{Charity sends signed BDIDs to DONAU}
 \begin{enumerate}
-  \item The charity verifies that the amount requested for signing is lower or 
equal to the effective amount of the donation.
-  \item The charity signs (using EdDSA) a structure containing all unsigned 
DUs coming from the donor. % Exactly: unsigned!
+\item The charity verifies that the amount requested (based on the $H(Px)$)
+      for signing is lower or equal to the effective amount of the donation.
+  \item The charity signs (using EdDSA) a structure containing all unsigned 
BDIDs coming from the donor.
   \item The charity sends this structure and the signature to the DONAU.
 \end{enumerate}
 
-\subsubsection{DONAU sends back blind signed DUs to charity}
+\subsubsection{DONAU sends back blind signed UDIDs to charity}
 \begin{enumerate}
   \item The DONAU:
     \begin{enumerate}
-      \item verifies the charity Signature on the structure.
-      \item increments the current year amount of the charity by the total 
amount of the BDR, if the increment does not exceed the annual limit.
-      \item blind signs (using RSA/Schnorr) all the DUs
+      \item verifies the charity signature on the structure.
+      \item increments the current year amount of the charity by the total 
amount of the BDIDs, if the increment does not exceed the annual limit.
+      \item blind signs all the BDIDs using the private keys $k_i$ matching 
the public keys $H(Pi)$
         \begin{align}
-          BS1_{k1} = sign(BDU1, k1)
-          BS2_{k4} = sign(BDU2, k4)
+          BS1 &:= sign(BU1, k_1) \\
+          BS2 &:= sign(BU2, k_4)
         \end{align}
-      \item sends back the blind signed DUs to the charity
+      \item sends back the blind signatures to the charity
     \end{enumerate}
-  \item The charity transmits the blind signed DUs to the donor.
+  \item The charity transmits the blind signatures to the donor.
   \item The donor unblinds the signatures.
   \begin{align}
-    S1_{k1} = unblind(BS1_{k1}, b_1) \\
-    S2_{k4} = unblind(BS2_{k4}, b_2)
+    S1_{k1} &= unblind(BS1, b_1) \\
+    S2_{k4} &= unblind(BS2, b_2)
   \end{align}
 \end{enumerate}
 
 
 \subsection{Step 2: Donor sends DR to DONAU, DONAU sends back donation 
statement (DS)}
 \begin{enumerate}
-  \item The donor sends the collection of all $(DUi, Si, kj)$ to the DONAU. 
The DR is always sent to the DONAU right after the donor has unblinded the DUs.
-  \item For each $(DUi, Si, kj)$ The DONAU...
+  \item The donor sends the collection of all $\langle BDUIi, Si, H(Pj) 
\rangle$ to the DONAU. The DR is always sent to the DONAU right after the donor 
has unblinded the DUs.
+  \item For each $\langle DUi, Si, H(Pj) \rangle$ The DONAU...
 
   \begin{itemize}
-    \item check if $kj$ is stored and get the corresponding year.
-    \item verifies if $Si$ is a correct signature with the corresponding 
secret key.
+    \item check if $Pj$ is stored and get the corresponding year and donation 
unit (amount donated).
+    \item verifies if $Si$ is a correct signature with the corresponding 
public key $Pj$.
     \item verifies that the hash of the TAXID and the salt is the same as in 
other DUs (how to solve the problem with multiple wallets?) % => Each wallet 
must simply obtain a separate DS!
     \item verifies that the nonce is different from each ever used nonce of 
this donor for the corresponding year.
     \item if all of this is the case, it adds the amount corresponding to the 
public key to the total donation amount for the year.
@@ -118,7 +127,7 @@ The NONCE is used to uniquely distinguish DU of the same 
value ("create a fresh
   year and hashed TAXID+salt and sends signature and the total amount so far 
back to the donor.
 
   \begin{align}
-    DS = sign(total amount, year, hash(TAXID, salt))
+    DS := sign(total amount, year, H(TAXID, salt))
   \end{align}
 
 \end{enumerate}
@@ -133,7 +142,6 @@ The NONCE is used to uniquely distinguish DU of the same 
value ("create a fresh
     \item DS received from the DONAU
     \item year
     \item amount for the year
-
   \end{itemize}
 
 \item The validator scans the QR code and validates that the signature 
corresponds to the current DONAU DS signing key.

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