diff --git a/contracts/Proofs.sol b/contracts/Proofs.sol
new file mode 100644
index 0000000..7ca7e94
--- /dev/null
+++ b/contracts/Proofs.sol
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+contract Proofs {
+
+  mapping(bytes32=>bool) private ids;
+  mapping(bytes32=>uint) private periods;
+  mapping(bytes32=>uint) private timeouts;
+  mapping(bytes32=>uint) private markers;
+  mapping(bytes32=>uint) private missed;
+  mapping(bytes32=>mapping(uint=>bool)) private received;
+  mapping(bytes32=>mapping(uint=>bool)) private missing;
+
+  function _period(bytes32 id) internal view returns (uint) {
+    return periods[id];
+  }
+
+  function _timeout(bytes32 id) internal view returns (uint) {
+    return timeouts[id];
+  }
+
+  function _missed(bytes32 id) internal view returns (uint) {
+    return missed[id];
+  }
+
+  function _expectProofs(bytes32 id, uint period, uint timeout) internal {
+    require(!ids[id], "Proof id already in use");
+    ids[id] = true;
+    periods[id] = period;
+    timeouts[id] = timeout;
+    markers[id] = uint(blockhash(block.number - 1)) % period;
+  }
+
+  function _isProofRequired(
+    bytes32 id,
+    uint blocknumber
+  )
+    internal view
+    returns (bool)
+  {
+    bytes32 hash = blockhash(blocknumber);
+    return hash != 0 && uint(hash) % periods[id] == markers[id];
+  }
+
+  function _isProofTimedOut(
+    bytes32 id,
+    uint blocknumber
+  )
+    internal view
+    returns (bool)
+  {
+    return block.number >= blocknumber + timeouts[id];
+  }
+
+  function _submitProof(
+    bytes32 id,
+    uint blocknumber,
+    bool proof
+  )
+    internal
+  {
+    require(proof, "Invalid proof"); // TODO: replace bool by actual proof
+    require(
+      _isProofRequired(id, blocknumber),
+      "No proof required for this block"
+    );
+    require(
+      !_isProofTimedOut(id, blocknumber),
+      "Proof not allowed after timeout"
+    );
+    require(!received[id][blocknumber], "Proof already submitted");
+    received[id][blocknumber] = true;
+  }
+
+  function _markProofAsMissing(bytes32 id, uint blocknumber) internal {
+    require(
+      _isProofTimedOut(id, blocknumber),
+      "Proof has not timed out yet"
+    );
+    require(
+      !received[id][blocknumber],
+      "Proof was submitted, not missing"
+    );
+    require(
+      _isProofRequired(id, blocknumber),
+      "Proof was not required"
+    );
+    require(!missing[id][blocknumber], "Proof already marked as missing");
+    missing[id][blocknumber] = true;
+    missed[id] += 1;
+  }
+}
diff --git a/contracts/StorageContracts.sol b/contracts/StorageContracts.sol
index 8643b4f..5d57d5e 100644
--- a/contracts/StorageContracts.sol
+++ b/contracts/StorageContracts.sol
@@ -2,8 +2,9 @@
 pragma solidity ^0.8.0;
 
 import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
+import "./Proofs.sol";
 
-contract StorageContracts {
+contract StorageContracts is Proofs {
 
   struct Contract {
     bool initialized; // always true, except for empty contracts in mapping
@@ -12,12 +13,6 @@ contract StorageContracts {
     bytes32 contentHash; // hash of data that is to be stored
     uint price; // price in coins
     address host; // host that provides storage
-    uint proofPeriod; // average time between proofs (in blocks)
-    uint proofTimeout; // proof has to be submitted before this
-    uint proofMarker; // indicates when a proof is required
-    mapping(uint => bool) proofReceived; // whether proof for block was received
-    mapping(uint => bool) proofMissing; // whether proof for block was missing
-    uint missingProofs;
   }
 
   uint numberOfContracts;
@@ -44,15 +39,15 @@ contract StorageContracts {
   }
 
   function proofPeriod(bytes32 contractId) public view returns (uint) {
-    return contracts[contractId].proofPeriod;
+    return _period(contractId);
   }
 
   function proofTimeout(bytes32 contractId) public view returns (uint) {
-    return contracts[contractId].proofTimeout;
+    return _timeout(contractId);
   }
 
   function missingProofs(bytes32 contractId) public view returns (uint) {
-    return contracts[contractId].missingProofs;
+    return _missed(contractId);
   }
 
   function newContract(
@@ -92,9 +87,7 @@ contract StorageContracts {
     c.price = _price;
     c.contentHash = _contentHash;
     c.host = _host;
-    c.proofPeriod = _proofPeriod;
-    c.proofTimeout = _proofTimeout;
-    c.proofMarker = uint(blockhash(block.number - 1)) % _proofPeriod;
+    _expectProofs(contractId, _proofPeriod, _proofTimeout);
   }
 
   // Creates hash for a storage request that can be used to check its signature.
@@ -171,20 +164,17 @@ contract StorageContracts {
     public view
     returns (bool)
   {
-    Contract storage c = contracts[contractId];
-    bytes32 hash = blockhash(blocknumber);
-    return hash != 0 && uint(hash) % c.proofPeriod == c.proofMarker;
+    return _isProofRequired(contractId, blocknumber);
   }
 
   function isProofTimedOut(
     bytes32 contractId,
     uint blocknumber
   )
-    internal view
+    public view
     returns (bool)
   {
-    Contract storage c = contracts[contractId];
-    return block.number >= blocknumber + c.proofTimeout;
+    return _isProofTimedOut(contractId, blocknumber);
   }
 
   function submitProof(
@@ -194,36 +184,10 @@ contract StorageContracts {
   )
     public
   {
-    Contract storage c = contracts[contractId];
-    require(proof, "Invalid proof"); // TODO: replace bool by actual proof
-    require(
-      isProofRequired(contractId, blocknumber),
-      "No proof required for this block"
-    );
-    require(
-      !isProofTimedOut(contractId, blocknumber),
-      "Proof not allowed after timeout"
-    );
-    require(!c.proofReceived[blocknumber], "Proof already submitted");
-    c.proofReceived[blocknumber] = true;
+    _submitProof(contractId, blocknumber, proof);
   }
 
   function markProofAsMissing(bytes32 contractId, uint blocknumber) public {
-    Contract storage c = contracts[contractId];
-    require(
-      isProofTimedOut(contractId, blocknumber),
-      "Proof has not timed out yet"
-    );
-    require(
-      !c.proofReceived[blocknumber],
-      "Proof was submitted, not missing"
-    );
-    require(
-      isProofRequired(contractId, blocknumber),
-      "Proof was not required"
-    );
-    require(!c.proofMissing[blocknumber], "Proof already marked as missing");
-    c.proofMissing[blocknumber] = true;
-    c.missingProofs += 1;
+    _markProofAsMissing(contractId, blocknumber);
   }
 }
diff --git a/contracts/TestProofs.sol b/contracts/TestProofs.sol
new file mode 100644
index 0000000..07b33dd
--- /dev/null
+++ b/contracts/TestProofs.sol
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "./Proofs.sol";
+
+// exposes internal functions of Proofs for testing
+contract TestProofs is Proofs {
+
+  function period(bytes32 id) public view returns (uint) {
+    return _period(id);
+  }
+
+  function timeout(bytes32 id) public view returns (uint) {
+    return _timeout(id);
+  }
+
+  function missed(bytes32 id) public view returns (uint) {
+    return _missed(id);
+  }
+
+  function expectProofs(bytes32 id, uint _period, uint _timeout) public {
+    _expectProofs(id, _period, _timeout);
+  }
+
+  function isProofRequired(
+    bytes32 id,
+    uint blocknumber
+  )
+    public view
+    returns (bool)
+  {
+    return _isProofRequired(id, blocknumber);
+  }
+
+  function submitProof(
+    bytes32 id,
+    uint blocknumber,
+    bool proof
+  )
+    public
+  {
+    _submitProof(id, blocknumber, proof);
+  }
+
+  function markProofAsMissing(bytes32 id, uint blocknumber) public {
+      _markProofAsMissing(id, blocknumber);
+  }
+}
diff --git a/test/Proofs.test.js b/test/Proofs.test.js
new file mode 100644
index 0000000..24e7c6b
--- /dev/null
+++ b/test/Proofs.test.js
@@ -0,0 +1,169 @@
+const { expect } = require("chai")
+const { ethers } = require("hardhat")
+
+describe("Proofs", function () {
+
+  const id = ethers.utils.randomBytes(32)
+  const period = 10
+  const timeout = 5
+
+  let proofs
+
+  beforeEach(async function () {
+    const Proofs = await ethers.getContractFactory("TestProofs")
+    proofs = await Proofs.deploy()
+  })
+
+  it("indicates that proofs are required", async function() {
+    await proofs.expectProofs(id, period, timeout)
+    expect(await proofs.period(id)).to.equal(period)
+    expect(await proofs.timeout(id)).to.equal(timeout)
+  })
+
+  it("does not allow ids to be reused", async function() {
+    await proofs.expectProofs(id, period, timeout)
+    await expect(
+      proofs.expectProofs(id, period, timeout)
+    ).to.be.revertedWith("Proof id already in use")
+  })
+
+  describe("when proofs are required", async function () {
+
+    beforeEach(async function () {
+      await proofs.expectProofs(id, period, timeout)
+    })
+
+    async function mineBlock() {
+      await ethers.provider.send("evm_mine")
+    }
+
+    async function minedBlockNumber() {
+      return await ethers.provider.getBlockNumber() - 1
+    }
+
+    async function mineUntilProofIsRequired(id) {
+      while (!await proofs.isProofRequired(id, await minedBlockNumber())) {
+        mineBlock()
+      }
+    }
+
+    async function mineUntilProofTimeout() {
+      for (let i=0; i<timeout; i++) {
+        mineBlock()
+      }
+    }
+
+    it("requires on average a proof every period", async function () {
+      let blocks = 500
+      let amount = 0
+      for (i=0; i<blocks; i++) {
+        await mineBlock()
+        if (await proofs.isProofRequired(id, await minedBlockNumber())) {
+          amount += 1
+        }
+      }
+      let average = blocks / amount
+      expect(average).to.be.closeTo(period, period / 2)
+    })
+
+    it("requires no proof for blocks that are unavailable", async function () {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      for (i=0; i<256; i++) { // only last 256 blocks are available in solidity
+        mineBlock()
+      }
+      expect(await proofs.isProofRequired(id, blocknumber)).to.be.false
+    })
+
+    it("submits a correct proof", async function () {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await proofs.submitProof(id, blocknumber, true)
+    })
+
+    it("fails proof submission when proof is incorrect", async function () {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await expect(
+        proofs.submitProof(id, blocknumber, false)
+      ).to.be.revertedWith("Invalid proof")
+    })
+
+    it("fails proof submission when proof was not required", async function () {
+      while (await proofs.isProofRequired(id, await minedBlockNumber())) {
+        await mineBlock()
+      }
+      let blocknumber = await minedBlockNumber()
+      await expect(
+        proofs.submitProof(id, blocknumber, true)
+      ).to.be.revertedWith("No proof required")
+    })
+
+    it("fails proof submission when proof is too late", async function () {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await mineUntilProofTimeout()
+      await expect(
+        proofs.submitProof(id, blocknumber, true)
+      ).to.be.revertedWith("Proof not allowed after timeout")
+    })
+
+    it("fails proof submission when already submitted", async function() {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await proofs.submitProof(id, blocknumber, true)
+      await expect(
+        proofs.submitProof(id, blocknumber, true)
+      ).to.be.revertedWith("Proof already submitted")
+    })
+
+    it("marks a proof as missing", async function () {
+      expect(await proofs.missed(id)).to.equal(0)
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await mineUntilProofTimeout()
+      await proofs.markProofAsMissing(id, blocknumber)
+      expect(await proofs.missed(id)).to.equal(1)
+    })
+
+    it("does not mark a proof as missing before timeout", async function () {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await mineBlock()
+      await expect(
+        proofs.markProofAsMissing(id, blocknumber)
+      ).to.be.revertedWith("Proof has not timed out yet")
+    })
+
+    it("does not mark a submitted proof as missing", async function () {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await proofs.submitProof(id, blocknumber, true)
+      await mineUntilProofTimeout()
+      await expect(
+        proofs.markProofAsMissing(id, blocknumber)
+      ).to.be.revertedWith("Proof was submitted, not missing")
+    })
+
+    it("does not mark proof as missing when not required", async function () {
+      while (await proofs.isProofRequired(id, await minedBlockNumber())) {
+        mineBlock()
+      }
+      let blocknumber = await minedBlockNumber()
+      await mineUntilProofTimeout()
+      await expect(
+        proofs.markProofAsMissing(id, blocknumber)
+      ).to.be.revertedWith("Proof was not required")
+    })
+
+    it("does not mark proof as missing twice", async function () {
+      await mineUntilProofIsRequired(id)
+      let blocknumber = await minedBlockNumber()
+      await mineUntilProofTimeout()
+      await proofs.markProofAsMissing(id, blocknumber)
+      await expect(
+        proofs.markProofAsMissing(id, blocknumber)
+      ).to.be.revertedWith("Proof already marked as missing")
+    })
+  })
+})
diff --git a/test/StorageContracts.test.js b/test/StorageContracts.test.js
index 4c402f6..a107905 100644
--- a/test/StorageContracts.test.js
+++ b/test/StorageContracts.test.js
@@ -197,158 +197,6 @@ describe("Storage Contracts", function () {
       await sign(host, bidHash),
     )).to.be.revertedWith("Bid expired")
   })
-
-  describe("proofs", function () {
-
-    async function mineBlock() {
-      await ethers.provider.send("evm_mine")
-    }
-
-    async function minedBlockNumber() {
-      return await ethers.provider.getBlockNumber() - 1
-    }
-
-    async function mineUntilProofIsRequired(id) {
-      while (!await contracts.isProofRequired(id, await minedBlockNumber())) {
-        mineBlock()
-      }
-    }
-
-    async function mineUntilProofTimeout() {
-      for (let i=0; i<proofTimeout; i++) {
-        mineBlock()
-      }
-    }
-
-    beforeEach(async function () {
-      await contracts.newContract(
-        duration,
-        size,
-        contentHash,
-        price,
-        proofPeriod,
-        proofTimeout,
-        nonce,
-        bidExpiry,
-        await host.getAddress(),
-        await sign(client, requestHash),
-        await sign(host, bidHash)
-      )
-    })
-
-    it("requires on average a proof every period", async function () {
-      let blocks = 400
-      let proofs = 0
-      for (i=0; i<blocks; i++) {
-        await mineBlock()
-        if (await contracts.isProofRequired(id, await minedBlockNumber())) {
-          proofs += 1
-        }
-      }
-      let average = blocks / proofs
-      expect(average).to.be.closeTo(proofPeriod, proofPeriod / 2)
-    })
-
-    it("requires no proof for blocks that are unavailable", async function () {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      for (i=0; i<256; i++) { // only last 256 blocks are available in solidity
-        mineBlock()
-      }
-      expect(await contracts.isProofRequired(id, blocknumber)).to.be.false
-    })
-
-    it("submits a correct proof", async function () {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await contracts.submitProof(id, blocknumber, true)
-    })
-
-    it("fails proof submission when proof is incorrect", async function () {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await expect(
-        contracts.submitProof(id, blocknumber, false)
-      ).to.be.revertedWith("Invalid proof")
-    })
-
-    it("fails proof submission when proof was not required", async function () {
-      while (await contracts.isProofRequired(id, await minedBlockNumber())) {
-        await mineBlock()
-      }
-      let blocknumber = await minedBlockNumber()
-      await expect(
-        contracts.submitProof(id, blocknumber, true)
-      ).to.be.revertedWith("No proof required")
-    })
-
-    it("fails proof submission when proof is too late", async function () {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await mineUntilProofTimeout()
-      await expect(
-        contracts.submitProof(id, blocknumber, true)
-      ).to.be.revertedWith("Proof not allowed after timeout")
-    })
-
-    it("fails proof submission when already submitted", async function() {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await contracts.submitProof(id, blocknumber, true)
-      await expect(
-        contracts.submitProof(id, blocknumber, true)
-      ).to.be.revertedWith("Proof already submitted")
-    })
-
-    it("marks a proof as missing", async function () {
-      expect(await contracts.missingProofs(id)).to.equal(0)
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await mineUntilProofTimeout()
-      await contracts.markProofAsMissing(id, blocknumber)
-      expect(await contracts.missingProofs(id)).to.equal(1)
-    })
-
-    it("does not mark a proof as missing before timeout", async function () {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await mineBlock()
-      await expect(
-        contracts.markProofAsMissing(id, blocknumber)
-      ).to.be.revertedWith("Proof has not timed out yet")
-    })
-
-    it("does not mark a submitted proof as missing", async function () {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await contracts.submitProof(id, blocknumber, true)
-      await mineUntilProofTimeout()
-      await expect(
-        contracts.markProofAsMissing(id, blocknumber)
-      ).to.be.revertedWith("Proof was submitted, not missing")
-    })
-
-    it("does not mark proof as missing when not required", async function () {
-      while (await contracts.isProofRequired(id, await minedBlockNumber())) {
-        mineBlock()
-      }
-      let blocknumber = await minedBlockNumber()
-      await mineUntilProofTimeout()
-      await expect(
-        contracts.markProofAsMissing(id, blocknumber)
-      ).to.be.revertedWith("Proof was not required")
-    })
-
-    it("does not mark proof as missing twice", async function () {
-      await mineUntilProofIsRequired(id)
-      let blocknumber = await minedBlockNumber()
-      await mineUntilProofTimeout()
-      await contracts.markProofAsMissing(id, blocknumber)
-      await expect(
-        contracts.markProofAsMissing(id, blocknumber)
-      ).to.be.revertedWith("Proof already marked as missing")
-    })
-  })
 })
 
 // TODO: implement checking of actual proofs of storage, instead of dummy bool