From 329039efb349f1258a9ebbb1c72767224092f867 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96zg=C3=BCr=20Kesim?= <oec@codeblau.de>
Date: Sun, 17 Oct 2021 18:18:55 +0200
Subject: [PATCH] first steps.

---
 cmd/taler-auditor-offline-signing/main.go | 77 +++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/cmd/taler-auditor-offline-signing/main.go b/cmd/taler-auditor-offline-signing/main.go
index 330934e..c997165 100644
--- a/cmd/taler-auditor-offline-signing/main.go
+++ b/cmd/taler-auditor-offline-signing/main.go
@@ -1,5 +1,82 @@
 package main
 
+import (
+	"crypto/rsa"
+	"encoding/binary"
+	"fmt"
+	"math/big"
+)
+
+type Keys struct {
+	Denoms          []DenomKey      `json:"denoms"`
+	MasterPublicKey MasterPublicKey `json:"master_public_key"`
+}
+
+type MasterPublicKey [256 / 8]byte
+
+type DenomKey struct {
+	DenomPub            EncodedRSAPublicKey `json:"denom_pub"`
+	Value               Amount              `json:"value"`
+	FeeWithdraw         Amount              `json:"fee_withdraw"`
+	FeeDeposit          Amount              `json:"fee_deposit"`
+	FeeRefresh          Amount              `json:"fee_refresh"`
+	FeeRefund           Amount              `json:"fee_refund"`
+	StampStart          AbsoluteTime        `json:"stamp_start"`
+	StampExpireWithdraw AbsoluteTime        `json:"stamp_expire_withdraw"`
+	StampExpireDeposit  AbsoluteTime        `json:"stamp_expire_deposit"`
+	StampExpireLegal    AbsoluteTime        `json:"stamp_expire_legal"`
+	MasterSig           EdDSASignature      `json:"master_sig"`
+}
+
+type EncodedRSAPublicKey []byte
+
+const (
+	CURRENCY_LEN     = 12
+	CURRENCY_LEN_STR = "12"
+)
+
+type Amount struct {
+	Value    uint64             `json:"value"`
+	Fraction uint32             `json:"fraction"`
+	Currency [CURRENCY_LEN]byte `json:"currency"`
+}
+
+type AbsoluteTime uint64
+
+type EdDSASignature struct {
+	R [256 / 8]byte `json:"r"`
+	S [256 / 8]byte `json:"s"`
+}
+
+// following gnunet/src/util/crypto_rsa.c
+func (ep *EncodedRSAPublicKey) Decode() (p rsa.PublicKey, e error) {
+	buf := []byte(*ep)
+	if len(buf) < 4 {
+		e = fmt.Errorf("byte array too small for RSA public key header")
+		return
+	}
+
+	modulus_length, public_exponent_length := binary.BigEndian.Uint16(buf[0:]), binary.BigEndian.Uint16(buf[2:])
+	if len(buf[4:]) != int(modulus_length)+int(public_exponent_length) {
+		e = fmt.Errorf("byte array has wrong size according to encoded length's for modulus and public exponent")
+		return
+	}
+
+	// BUG! This is most likely wrong.
+	// Consult _gcry_mpi_set_buffer from libgcrypt-1.9.4/mpi/mpicoder.c
+	buf = buf[4:]
+	p.N = big.NewInt(0).SetBytes(buf[:modulus_length])
+	buf = buf[modulus_length:]
+	ex := big.NewInt(0).SetBytes(buf[:public_exponent_length]) // binary.BigEndian.Uint64 instead?
+	if !ex.IsInt64() {
+		e = fmt.Errorf("public exponent is not int64")
+		return
+	}
+	p.E = int(ex.Int64())
+
+	return p, e
+}
+
 func main() {
 	panic("nothing implemented yet.")
 }