diff --git a/content_scripts/notify.ts b/content_scripts/notify.ts
index abc72616c..e50c93c4d 100644
--- a/content_scripts/notify.ts
+++ b/content_scripts/notify.ts
@@ -76,8 +76,8 @@ namespace TalerNotify {
         console.log("it's execute");
         document.documentElement.style.visibility = "hidden";
         taler.internalExecutePayment(resp.contractHash,
-                                      resp.payUrl,
-                                      resp.offerUrl);
+                                     resp.payUrl,
+                                     resp.offerUrl);
       }
     });
   }
@@ -163,38 +163,62 @@ namespace TalerNotify {
         return;
       }
 
-      const walletMsg = {
-        type: "check-repurchase",
-        detail: {
-          contract: offer.contract
-        },
+      if (!offer.H_contract) {
+        console.error("H_contract field missing");
+        return;
+      }
+
+      let walletHashContractMsg = {
+        type: "hash-contract",
+        detail: {contract: offer.contract}
       };
 
-      chrome.runtime.sendMessage(walletMsg, (resp: any) => {
-        if (resp.error) {
-          console.error("wallet backend error", resp);
+      chrome.runtime.sendMessage(walletHashContractMsg, (resp: any) => {
+
+        if (!resp.hash) {
+          console.log("error", resp);
+          throw Error("hashing failed");
+        }
+
+        if (resp.hash != offer.H_contract) {
+          console.error("merchant-supplied contract hash is wrong");
           return;
         }
-        if (resp.isRepurchase) {
-          console.log("doing repurchase");
-          console.assert(resp.existingFulfillmentUrl);
-          console.assert(resp.existingContractHash);
-          window.location.href = subst(resp.existingFulfillmentUrl,
-                                       resp.existingContractHash);
 
-        } else {
-          const uri = URI(chrome.extension.getURL("pages/confirm-contract.html"));
-          const params = {
-            offer: JSON.stringify(offer),
-            merchantPageUrl: document.location.href,
-          };
-          const target = uri.query(params).href();
-          if (msg.replace_navigation === true) {
-            document.location.replace(target);
-          } else {
-            document.location.href = target;
+        const walletMsg = {
+          type: "check-repurchase",
+          detail: {
+            contract: offer.contract
+          },
+        };
+
+        chrome.runtime.sendMessage(walletMsg, (resp: any) => {
+          if (resp.error) {
+            console.error("wallet backend error", resp);
+            return;
           }
-        }
+          if (resp.isRepurchase) {
+            console.log("doing repurchase");
+            console.assert(resp.existingFulfillmentUrl);
+            console.assert(resp.existingContractHash);
+            window.location.href = subst(resp.existingFulfillmentUrl,
+                                         resp.existingContractHash);
+
+          } else {
+            const uri = URI(chrome.extension.getURL(
+              "pages/confirm-contract.html"));
+            const params = {
+              offer: JSON.stringify(offer),
+              merchantPageUrl: document.location.href,
+            };
+            const target = uri.query(params).href();
+            if (msg.replace_navigation === true) {
+              document.location.replace(target);
+            } else {
+              document.location.href = target;
+            }
+          }
+        });
       });
     });
 
diff --git a/lib/emscripten/emsc.d.ts b/lib/emscripten/emsc.d.ts
index 19a6990e5..b9690433f 100644
--- a/lib/emscripten/emsc.d.ts
+++ b/lib/emscripten/emsc.d.ts
@@ -33,6 +33,8 @@ export interface EmscFunGen {
 export declare namespace Module {
   var cwrap: EmscFunGen;
 
+  function stringToUTF8(s: string, addr: number, maxLength: number): void
+
   function _free(ptr: number): void;
 
   function _malloc(n: number): number;
diff --git a/lib/wallet/cryptoApi.ts b/lib/wallet/cryptoApi.ts
index 585aa39e7..db29592fc 100644
--- a/lib/wallet/cryptoApi.ts
+++ b/lib/wallet/cryptoApi.ts
@@ -176,6 +176,10 @@ export class CryptoApi {
     return this.doRpc("createPreCoin", 1, denom, reserve);
   }
 
+  hashString(str: string): Promise<string> {
+    return this.doRpc("hashString", 1, str);
+  }
+
   hashRsaPub(rsaPub: string): Promise<string> {
     return this.doRpc("hashRsaPub", 2, rsaPub);
   }
diff --git a/lib/wallet/cryptoLib.ts b/lib/wallet/cryptoLib.ts
index 58a3d5004..9a77b3d74 100644
--- a/lib/wallet/cryptoLib.ts
+++ b/lib/wallet/cryptoLib.ts
@@ -139,6 +139,11 @@ namespace RpcFunctions {
 
   }
 
+  export function hashString(str: string): string {
+    const b = native.ByteArray.fromString(str);
+    return b.hash().toCrock();
+  }
+
 
   export function hashRsaPub(rsaPub: string): string {
     return native.RsaPublicKey.fromCrock(rsaPub)
diff --git a/lib/wallet/emscriptif.ts b/lib/wallet/emscriptif.ts
index 1e5fb0283..9a1d902c0 100644
--- a/lib/wallet/emscriptif.ts
+++ b/lib/wallet/emscriptif.ts
@@ -36,8 +36,9 @@ const GNUNET_SYSERR = -1;
 
 let Module = EmscWrapper.Module;
 
-let getEmsc: EmscWrapper.EmscFunGen = (...args: any[]) => Module.cwrap.apply(null,
-                                                                      args);
+let getEmsc: EmscWrapper.EmscFunGen = (...args: any[]) => Module.cwrap.apply(
+  null,
+  args);
 
 var emsc = {
   free: (ptr: number) => Module._free(ptr),
@@ -395,6 +396,30 @@ export class Amount extends ArenaObject {
 }
 
 
+/**
+ * Count the UTF-8 characters in a JavaScript string.
+ */
+function countBytes(str: string): number {
+  var s = str.length;
+  // JavaScript strings are UTF-16 arrays
+  for (let i = str.length - 1; i >= 0; i--) {
+    var code = str.charCodeAt(i);
+    if (code > 0x7f && code <= 0x7ff) {
+      // We need an extra byte in utf-8 here
+      s++;
+    } else if (code > 0x7ff && code <= 0xffff) {
+      // We need two extra bytes in utf-8 here
+      s += 2;
+    }
+    // Skip over the other surrogate
+    if (code >= 0xDC00 && code <= 0xDFFF) {
+      i--;
+    }
+  }
+  return s;
+}
+
+
 /**
  * Managed reference to a contiguous block of memory in the Emscripten heap.
  * Should contain only data, not pointers.
@@ -632,17 +657,20 @@ export class ByteArray extends PackedArenaObject {
   }
 
   static fromString(s: string, a?: Arena): ByteArray {
-    let hstr = emscAlloc.malloc(s.length + 1);
-    Module.writeStringToMemory(s, hstr);
-    return new ByteArray(s.length, hstr, a);
+    // UTF-8 bytes, including 0-terminator
+    let terminatedByteLength = countBytes(s) + 1;
+    let hstr = emscAlloc.malloc(terminatedByteLength);
+    Module.stringToUTF8(s, hstr, terminatedByteLength);
+    return new ByteArray(terminatedByteLength, hstr, a);
   }
 
   static fromCrock(s: string, a?: Arena): ByteArray {
-    let hstr = emscAlloc.malloc(s.length + 1);
-    Module.writeStringToMemory(s, hstr);
-    let decodedLen = Math.floor((s.length * 5) / 8);
+    let byteLength = countBytes(s) + 1;
+    let hstr = emscAlloc.malloc(byteLength);
+    Module.stringToUTF8(s, hstr, byteLength);
+    let decodedLen = Math.floor((byteLength * 5) / 8);
     let ba = new ByteArray(decodedLen, undefined, a);
-    let res = emsc.string_to_data(hstr, s.length, ba.nativePtr, decodedLen);
+    let res = emsc.string_to_data(hstr, byteLength, ba.nativePtr, decodedLen);
     emsc.free(hstr);
     if (res != GNUNET_OK) {
       throw Error("decoding failed");
diff --git a/lib/wallet/wallet.ts b/lib/wallet/wallet.ts
index 35f86399a..0a2c07673 100644
--- a/lib/wallet/wallet.ts
+++ b/lib/wallet/wallet.ts
@@ -45,12 +45,22 @@ import {ExchangeHandle} from "./types";
 
 "use strict";
 
-
 export interface CoinWithDenom {
   coin: Coin;
   denom: Denomination;
 }
 
+interface ReserveRecord {
+  reserve_pub: string;
+  reserve_priv: string,
+  exchange_base_url: string,
+  created: number,
+  last_query: number|null,
+  current_amount: null,
+  requested_amount: AmountJson,
+  confirmed: boolean,
+}
+
 
 @Checkable.Class
 export class KeysJson {
@@ -124,6 +134,13 @@ export class Offer {
   static checked: (obj: any) => Offer;
 }
 
+export interface HistoryRecord {
+  type: string;
+  timestamp: number;
+  subjectId?: string;
+  detail: any;
+}
+
 
 interface ExchangeCoins {
   [exchangeUrl: string]: CoinWithDenom[];
@@ -145,6 +162,32 @@ export interface Badge {
   stopBusy(): void;
 }
 
+export function canonicalJson(obj: any): string {
+  // Check for cycles, etc.
+  JSON.stringify(obj);
+  if (typeof obj == "string" || typeof obj == "number" || obj === null) {
+    return JSON.stringify(obj)
+  }
+  if (Array.isArray(obj)) {
+    let objs: string[] = obj.map((e) => canonicalJson(e));
+    return `[${objs.join(',')}]`;
+  }
+  let keys: string[] = [];
+  for (let key in obj) {
+    keys.push(key);
+  }
+  keys.sort();
+  let s = "{";
+  for (let i = 0; i < keys.length; i++) {
+    let key = keys[i];
+    s += JSON.stringify(key) + ":" + canonicalJson(obj[key]);
+    if (i != keys.length - 1) {
+      s += ",";
+    }
+  }
+  return s + "}";
+}
+
 
 function deepEquals(x: any, y: any): boolean {
   if (x === y) {
@@ -467,6 +510,7 @@ export class Wallet {
     let historyEntry = {
       type: "pay",
       timestamp: (new Date).getTime(),
+      subjectId: `contract-${offer.H_contract}`,
       detail: {
         merchantName: offer.contract.merchant.name,
         amount: offer.contract.amount,
@@ -485,6 +529,11 @@ export class Wallet {
   }
 
 
+  async putHistory(historyEntry: HistoryRecord): Promise<void> {
+    await Query(this.db).put("history", historyEntry).finish();
+  }
+
+
   /**
    * Add a contract to the wallet and sign coins,
    * but do not send them yet.
@@ -574,7 +623,7 @@ export class Wallet {
    * First fetch information requred to withdraw from the reserve,
    * then deplete the reserve, withdrawing coins until it is empty.
    */
-  private async processReserve(reserveRecord: any,
+  private async processReserve(reserveRecord: ReserveRecord,
                                retryDelayMs: number = 250): Promise<void> {
     const opId = "reserve-" + reserveRecord.reserve_pub;
     this.startOperation(opId);
@@ -586,9 +635,11 @@ export class Wallet {
       await this.depleteReserve(reserve, exchange);
       let depleted = {
         type: "depleted-reserve",
+        subjectId: `reserve-progress-${reserveRecord.reserve_pub}`,
         timestamp: (new Date).getTime(),
         detail: {
           reservePub: reserveRecord.reserve_pub,
+          currentAmount: reserveRecord.current_amount,
         }
       };
       await Query(this.db).put("history", depleted).finish();
@@ -630,7 +681,7 @@ export class Wallet {
     const now = (new Date).getTime();
     const canonExchange = canonicalizeBaseUrl(req.exchange);
 
-    const reserveRecord = {
+    const reserveRecord: ReserveRecord = {
       reserve_pub: keypair.pub,
       reserve_priv: keypair.priv,
       exchange_base_url: canonExchange,
@@ -644,6 +695,7 @@ export class Wallet {
     const historyEntry = {
       type: "create-reserve",
       timestamp: now,
+      subjectId: `reserve-progress-${reserveRecord.reserve_pub}`,
       detail: {
         requestedAmount: req.amount,
         reservePub: reserveRecord.reserve_pub,
@@ -674,26 +726,28 @@ export class Wallet {
    */
   async confirmReserve(req: ConfirmReserveRequest): Promise<void> {
     const now = (new Date).getTime();
+    let reserve: ReserveRecord = await Query(this.db)
+      .get("reserves", req.reservePub);
     const historyEntry = {
       type: "confirm-reserve",
       timestamp: now,
+      subjectId: `reserve-progress-${reserve.reserve_pub}`,
       detail: {
         reservePub: req.reservePub,
+        requestedAmount: reserve.requested_amount,
       }
     };
-    let r = await Query(this.db)
-      .get("reserves", req.reservePub);
-    if (!r) {
+    if (!reserve) {
       console.error("Unable to confirm reserve, not found in DB");
       return;
     }
-    r.confirmed = true;
+    reserve.confirmed = true;
     await Query(this.db)
-      .put("reserves", r)
+      .put("reserves", reserve)
       .put("history", historyEntry)
       .finish();
 
-    this.processReserve(r);
+    this.processReserve(reserve);
   }
 
 
@@ -801,8 +855,10 @@ export class Wallet {
     let historyEntry = {
       type: "reserve-update",
       timestamp: (new Date).getTime(),
+      subjectId: `reserve-progress-${reserve.reserve_pub}`,
       detail: {
         reservePub,
+        requestedAmount: reserve.requested_amount,
         oldAmount,
         newAmount
       }
@@ -1040,6 +1096,10 @@ export class Wallet {
     return {history};
   }
 
+  async hashContract(contract: any): Promise<string> {
+    return this.cryptoApi.hashString(canonicalJson(contract));
+  }
+
   /**
    * Check if there's an equivalent contract we've already purchased.
    */
diff --git a/lib/wallet/wxMessaging.ts b/lib/wallet/wxMessaging.ts
index be0e09de7..5c97248c4 100644
--- a/lib/wallet/wxMessaging.ts
+++ b/lib/wallet/wxMessaging.ts
@@ -151,6 +151,20 @@ function makeHandlers(db: IDBDatabase,
       }
       return wallet.updateExchangeFromUrl(detail.baseUrl);
     },
+    ["hash-contract"]: function(detail) {
+      if (!detail.contract) {
+        return Promise.resolve({error: "contract missing"});
+      }
+      return wallet.hashContract(detail.contract).then((hash) => {
+        return {hash};
+      });
+    },
+    ["put-history-entry"]: function(detail: any) {
+      if (!detail.historyEntry) {
+        return Promise.resolve({error: "historyEntry missing"});
+      }
+      return wallet.putHistory(detail.historyEntry);
+    },
     ["reserve-creation-info"]: function(detail, sender) {
       if (!detail.baseUrl || typeof detail.baseUrl !== "string") {
         return Promise.resolve({error: "bad url"});
diff --git a/popup/popup.tsx b/popup/popup.tsx
index 5a381c987..3797d81dc 100644
--- a/popup/popup.tsx
+++ b/popup/popup.tsx
@@ -30,7 +30,7 @@
 
 import {substituteFulfillmentUrl} from "../lib/wallet/helpers";
 import BrowserClickedEvent = chrome.browserAction.BrowserClickedEvent;
-import {Wallet} from "../lib/wallet/wallet";
+import {HistoryRecord} from "../lib/wallet/wallet";
 import {AmountJson} from "../lib/wallet/types";
 
 declare var m: any;
@@ -173,7 +173,7 @@ function retryPayment(url: string, contractHash: string) {
 }
 
 
-function formatHistoryItem(historyItem: any) {
+function formatHistoryItem(historyItem: HistoryRecord) {
   const d = historyItem.detail;
   const t = historyItem.timestamp;
   console.log("hist item", historyItem);
@@ -215,7 +215,7 @@ namespace WalletHistory {
   }
 
   class Controller {
-    myHistory: any;
+    myHistory: any[];
     gotError = false;
 
     constructor() {
@@ -241,14 +241,24 @@ namespace WalletHistory {
   }
 
   export function view(ctrl: Controller) {
-    let history = ctrl.myHistory;
+    let history: HistoryRecord[] = ctrl.myHistory;
     if (ctrl.gotError) {
       return i18n`Error: could not retrieve event history`;
     }
     if (!history) {
       throw Error("Could not retrieve history");
     }
-    let listing = _.map(history, formatHistoryItem);
+
+    let subjectMemo: {[s: string]: boolean} = {};
+    let listing: any[] = [];
+    for (let record of history.reverse()) {
+      //if (record.subjectId && subjectMemo[record.subjectId]) {
+      //  return;
+      //}
+      subjectMemo[record.subjectId as string] = true;
+      listing.push(formatHistoryItem(record));
+    }
+
     if (listing.length > 0) {
       return m("div.container", listing);
     }