diff --git a/.gitignore b/.gitignore
index 98e6ef6..570133a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 *.db
+wallet.dat
diff --git a/README.md b/README.md
index 7c9b585..87fc9f4 100644
--- a/README.md
+++ b/README.md
@@ -6,3 +6,4 @@ A blockchain implementation in Go, as described in these articles:
 2. [Proof-of-Work](https://jeiwan.cc/posts/building-blockchain-in-go-part-2/)
 2. [Persistence and CLI](https://jeiwan.cc/posts/building-blockchain-in-go-part-3/)
 3. [Transactions 1](https://jeiwan.cc/posts/building-blockchain-in-go-part-4/)
+3. [Addresses](https://jeiwan.cc/posts/building-blockchain-in-go-part-5/)
diff --git a/base58.go b/base58.go
new file mode 100644
index 0000000..589e00c
--- /dev/null
+++ b/base58.go
@@ -0,0 +1,59 @@
+package main
+
+import (
+	"bytes"
+	"math/big"
+)
+
+var b58Alphabet = []byte("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz")
+
+// Base58Encode encodes a byte array to Base58
+func Base58Encode(input []byte) []byte {
+	var result []byte
+
+	x := big.NewInt(0).SetBytes(input)
+
+	base := big.NewInt(int64(len(b58Alphabet)))
+	zero := big.NewInt(0)
+	mod := &big.Int{}
+
+	for x.Cmp(zero) != 0 {
+		x.DivMod(x, base, mod)
+		result = append(result, b58Alphabet[mod.Int64()])
+	}
+
+	ReverseBytes(result)
+	for b := range input {
+		if b == 0x00 {
+			result = append([]byte{b58Alphabet[0]}, result...)
+		} else {
+			break
+		}
+	}
+
+	return result
+}
+
+// Base58Decode decodes Base58-encoded data
+func Base58Decode(input []byte) []byte {
+	result := big.NewInt(0)
+	zeroBytes := 0
+
+	for b := range input {
+		if b == 0x00 {
+			zeroBytes++
+		}
+	}
+
+	payload := input[zeroBytes:]
+	for _, b := range payload {
+		charIndex := bytes.IndexByte(b58Alphabet, b)
+		result.Mul(result, big.NewInt(58))
+		result.Add(result, big.NewInt(int64(charIndex)))
+	}
+
+	decoded := result.Bytes()
+	decoded = append(bytes.Repeat([]byte{byte(0x00)}, zeroBytes), decoded...)
+
+	return decoded
+}
diff --git a/block.go b/block.go
index 04d96cc..b98c79c 100644
--- a/block.go
+++ b/block.go
@@ -8,7 +8,7 @@ import (
 	"time"
 )
 
-// Block keeps block headers
+// Block represents a block in the blockchain
 type Block struct {
 	Timestamp     int64
 	Transactions  []*Transaction
@@ -17,32 +17,6 @@ type Block struct {
 	Nonce         int
 }
 
-// Serialize serializes the block
-func (b *Block) Serialize() []byte {
-	var result bytes.Buffer
-	encoder := gob.NewEncoder(&result)
-
-	err := encoder.Encode(b)
-	if err != nil {
-		log.Panic(err)
-	}
-
-	return result.Bytes()
-}
-
-// HashTransactions returns a hash of the transactions in the block
-func (b *Block) HashTransactions() []byte {
-	var txHashes [][]byte
-	var txHash [32]byte
-
-	for _, tx := range b.Transactions {
-		txHashes = append(txHashes, tx.ID)
-	}
-	txHash = sha256.Sum256(bytes.Join(txHashes, []byte{}))
-
-	return txHash[:]
-}
-
 // NewBlock creates and returns Block
 func NewBlock(transactions []*Transaction, prevBlockHash []byte) *Block {
 	block := &Block{time.Now().Unix(), transactions, prevBlockHash, []byte{}, 0}
@@ -60,6 +34,32 @@ func NewGenesisBlock(coinbase *Transaction) *Block {
 	return NewBlock([]*Transaction{coinbase}, []byte{})
 }
 
+// HashTransactions returns a hash of the transactions in the block
+func (b *Block) HashTransactions() []byte {
+	var txHashes [][]byte
+	var txHash [32]byte
+
+	for _, tx := range b.Transactions {
+		txHashes = append(txHashes, tx.Hash())
+	}
+	txHash = sha256.Sum256(bytes.Join(txHashes, []byte{}))
+
+	return txHash[:]
+}
+
+// Serialize serializes the block
+func (b *Block) Serialize() []byte {
+	var result bytes.Buffer
+	encoder := gob.NewEncoder(&result)
+
+	err := encoder.Encode(b)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	return result.Bytes()
+}
+
 // DeserializeBlock deserializes a block
 func DeserializeBlock(d []byte) *Block {
 	var block Block
diff --git a/blockchain.go b/blockchain.go
index b9cfb42..e2579fe 100644
--- a/blockchain.go
+++ b/blockchain.go
@@ -1,7 +1,10 @@
 package main
 
 import (
+	"bytes"
+	"crypto/ecdsa"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"log"
 	"os"
@@ -19,23 +22,210 @@ type Blockchain struct {
 	db  *bolt.DB
 }
 
-// BlockchainIterator is used to iterate over blockchain blocks
-type BlockchainIterator struct {
-	currentHash []byte
-	db          *bolt.DB
+// CreateBlockchain creates a new blockchain DB
+func CreateBlockchain(address string) *Blockchain {
+	if dbExists() {
+		fmt.Println("Blockchain already exists.")
+		os.Exit(1)
+	}
+
+	var tip []byte
+
+	cbtx := NewCoinbaseTX(address, genesisCoinbaseData)
+	genesis := NewGenesisBlock(cbtx)
+
+	db, err := bolt.Open(dbFile, 0600, nil)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	err = db.Update(func(tx *bolt.Tx) error {
+		b, err := tx.CreateBucket([]byte(blocksBucket))
+		if err != nil {
+			log.Panic(err)
+		}
+
+		err = b.Put(genesis.Hash, genesis.Serialize())
+		if err != nil {
+			log.Panic(err)
+		}
+
+		err = b.Put([]byte("l"), genesis.Hash)
+		if err != nil {
+			log.Panic(err)
+		}
+		tip = genesis.Hash
+
+		return nil
+	})
+	if err != nil {
+		log.Panic(err)
+	}
+
+	bc := Blockchain{tip, db}
+
+	return &bc
+}
+
+// NewBlockchain creates a new Blockchain with genesis Block
+func NewBlockchain(address string) *Blockchain {
+	if dbExists() == false {
+		fmt.Println("No existing blockchain found. Create one first.")
+		os.Exit(1)
+	}
+
+	var tip []byte
+	db, err := bolt.Open(dbFile, 0600, nil)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	err = db.Update(func(tx *bolt.Tx) error {
+		b := tx.Bucket([]byte(blocksBucket))
+		tip = b.Get([]byte("l"))
+
+		return nil
+	})
+	if err != nil {
+		log.Panic(err)
+	}
+
+	bc := Blockchain{tip, db}
+
+	return &bc
+}
+
+// FindSpendableOutputs finds and returns unspent outputs to reference in inputs
+func (bc *Blockchain) FindSpendableOutputs(pubKeyHash []byte, amount int) (int, map[string][]int) {
+	unspentOutputs := make(map[string][]int)
+	unspentTXs := bc.FindUnspentTransactions(pubKeyHash)
+	accumulated := 0
+
+Work:
+	for _, tx := range unspentTXs {
+		txID := hex.EncodeToString(tx.ID)
+
+		for outIdx, out := range tx.Vout {
+			if out.IsLockedWithKey(pubKeyHash) && accumulated < amount {
+				accumulated += out.Value
+				unspentOutputs[txID] = append(unspentOutputs[txID], outIdx)
+
+				if accumulated >= amount {
+					break Work
+				}
+			}
+		}
+	}
+
+	return accumulated, unspentOutputs
+}
+
+// FindTransaction finds a transaction by its ID
+func (bc *Blockchain) FindTransaction(ID []byte) (Transaction, error) {
+	bci := bc.Iterator()
+
+	for {
+		block := bci.Next()
+
+		for _, tx := range block.Transactions {
+			if bytes.Compare(tx.ID, ID) == 0 {
+				return *tx, nil
+			}
+		}
+
+		if len(block.PrevBlockHash) == 0 {
+			break
+		}
+	}
+
+	return Transaction{}, errors.New("Transaction is not found")
+}
+
+// FindUnspentTransactions returns a list of transactions containing unspent outputs
+func (bc *Blockchain) FindUnspentTransactions(pubKeyHash []byte) []Transaction {
+	var unspentTXs []Transaction
+	spentTXOs := make(map[string][]int)
+	bci := bc.Iterator()
+
+	for {
+		block := bci.Next()
+
+		for _, tx := range block.Transactions {
+			txID := hex.EncodeToString(tx.ID)
+
+		Outputs:
+			for outIdx, out := range tx.Vout {
+				// Was the output spent?
+				if spentTXOs[txID] != nil {
+					for _, spentOutIdx := range spentTXOs[txID] {
+						if spentOutIdx == outIdx {
+							continue Outputs
+						}
+					}
+				}
+
+				if out.IsLockedWithKey(pubKeyHash) {
+					unspentTXs = append(unspentTXs, *tx)
+				}
+			}
+
+			if tx.IsCoinbase() == false {
+				for _, in := range tx.Vin {
+					if in.UsesKey(pubKeyHash) {
+						inTxID := hex.EncodeToString(in.Txid)
+						spentTXOs[inTxID] = append(spentTXOs[inTxID], in.Vout)
+					}
+				}
+			}
+		}
+
+		if len(block.PrevBlockHash) == 0 {
+			break
+		}
+	}
+
+	return unspentTXs
+}
+
+// FindUTXO finds and returns all unspent transaction outputs
+func (bc *Blockchain) FindUTXO(pubKeyHash []byte) []TXOutput {
+	var UTXOs []TXOutput
+	unspentTransactions := bc.FindUnspentTransactions(pubKeyHash)
+
+	for _, tx := range unspentTransactions {
+		for _, out := range tx.Vout {
+			if out.IsLockedWithKey(pubKeyHash) {
+				UTXOs = append(UTXOs, out)
+			}
+		}
+	}
+
+	return UTXOs
+}
+
+// Iterator returns a BlockchainIterat
+func (bc *Blockchain) Iterator() *BlockchainIterator {
+	bci := &BlockchainIterator{bc.tip, bc.db}
+
+	return bci
 }
 
 // MineBlock mines a new block with the provided transactions
 func (bc *Blockchain) MineBlock(transactions []*Transaction) {
 	var lastHash []byte
 
+	for _, tx := range transactions {
+		if bc.VerifyTransaction(tx) != true {
+			log.Panic("ERROR: Invalid transaction")
+		}
+	}
+
 	err := bc.db.View(func(tx *bolt.Tx) error {
 		b := tx.Bucket([]byte(blocksBucket))
 		lastHash = b.Get([]byte("l"))
 
 		return nil
 	})
-
 	if err != nil {
 		log.Panic(err)
 	}
@@ -58,121 +248,39 @@ func (bc *Blockchain) MineBlock(transactions []*Transaction) {
 
 		return nil
 	})
-}
-
-// FindUnspentTransactions returns a list of transactions containing unspent outputs
-func (bc *Blockchain) FindUnspentTransactions(address string) []Transaction {
-	var unspentTXs []Transaction
-	spentTXOs := make(map[string][]int)
-	bci := bc.Iterator()
-
-	for {
-		block := bci.Next()
-
-		for _, tx := range block.Transactions {
-			txID := hex.EncodeToString(tx.ID)
-
-		Outputs:
-			for outIdx, out := range tx.Vout {
-				// Was the output spent?
-				if spentTXOs[txID] != nil {
-					for _, spentOut := range spentTXOs[txID] {
-						if spentOut == outIdx {
-							continue Outputs
-						}
-					}
-				}
-
-				if out.CanBeUnlockedWith(address) {
-					unspentTXs = append(unspentTXs, *tx)
-				}
-			}
-
-			if tx.IsCoinbase() == false {
-				for _, in := range tx.Vin {
-					if in.CanUnlockOutputWith(address) {
-						inTxID := hex.EncodeToString(in.Txid)
-						spentTXOs[inTxID] = append(spentTXOs[inTxID], in.Vout)
-					}
-				}
-			}
-		}
-
-		if len(block.PrevBlockHash) == 0 {
-			break
-		}
-	}
-
-	return unspentTXs
-}
-
-// FindUTXO finds and returns all unspent transaction outputs
-func (bc *Blockchain) FindUTXO(address string) []TXOutput {
-	var UTXOs []TXOutput
-	unspentTransactions := bc.FindUnspentTransactions(address)
-
-	for _, tx := range unspentTransactions {
-		for _, out := range tx.Vout {
-			if out.CanBeUnlockedWith(address) {
-				UTXOs = append(UTXOs, out)
-			}
-		}
-	}
-
-	return UTXOs
-}
-
-// FindSpendableOutputs finds and returns unspent outputs to reference in inputs
-func (bc *Blockchain) FindSpendableOutputs(address string, amount int) (int, map[string][]int) {
-	unspentOutputs := make(map[string][]int)
-	unspentTXs := bc.FindUnspentTransactions(address)
-	accumulated := 0
-
-Work:
-	for _, tx := range unspentTXs {
-		txID := hex.EncodeToString(tx.ID)
-
-		for outIdx, out := range tx.Vout {
-			if out.CanBeUnlockedWith(address) && accumulated < amount {
-				accumulated += out.Value
-				unspentOutputs[txID] = append(unspentOutputs[txID], outIdx)
-
-				if accumulated >= amount {
-					break Work
-				}
-			}
-		}
-	}
-
-	return accumulated, unspentOutputs
-}
-
-// Iterator returns a BlockchainIterat
-func (bc *Blockchain) Iterator() *BlockchainIterator {
-	bci := &BlockchainIterator{bc.tip, bc.db}
-
-	return bci
-}
-
-// Next returns next block starting from the tip
-func (i *BlockchainIterator) Next() *Block {
-	var block *Block
-
-	err := i.db.View(func(tx *bolt.Tx) error {
-		b := tx.Bucket([]byte(blocksBucket))
-		encodedBlock := b.Get(i.currentHash)
-		block = DeserializeBlock(encodedBlock)
-
-		return nil
-	})
-
 	if err != nil {
 		log.Panic(err)
 	}
+}
 
-	i.currentHash = block.PrevBlockHash
+// SignTransaction signs inputs of a Transaction
+func (bc *Blockchain) SignTransaction(tx *Transaction, privKey ecdsa.PrivateKey) {
+	prevTXs := make(map[string]Transaction)
 
-	return block
+	for _, vin := range tx.Vin {
+		prevTX, err := bc.FindTransaction(vin.Txid)
+		if err != nil {
+			log.Panic(err)
+		}
+		prevTXs[hex.EncodeToString(prevTX.ID)] = prevTX
+	}
+
+	tx.Sign(privKey, prevTXs)
+}
+
+// VerifyTransaction verifies transaction input signatures
+func (bc *Blockchain) VerifyTransaction(tx *Transaction) bool {
+	prevTXs := make(map[string]Transaction)
+
+	for _, vin := range tx.Vin {
+		prevTX, err := bc.FindTransaction(vin.Txid)
+		if err != nil {
+			log.Panic(err)
+		}
+		prevTXs[hex.EncodeToString(prevTX.ID)] = prevTX
+	}
+
+	return tx.Verify(prevTXs)
 }
 
 func dbExists() bool {
@@ -182,77 +290,3 @@ func dbExists() bool {
 
 	return true
 }
-
-// NewBlockchain creates a new Blockchain with genesis Block
-func NewBlockchain(address string) *Blockchain {
-	if dbExists() == false {
-		fmt.Println("No existing blockchain found. Create one first.")
-		os.Exit(1)
-	}
-
-	var tip []byte
-	db, err := bolt.Open(dbFile, 0600, nil)
-	if err != nil {
-		log.Panic(err)
-	}
-
-	err = db.Update(func(tx *bolt.Tx) error {
-		b := tx.Bucket([]byte(blocksBucket))
-		tip = b.Get([]byte("l"))
-
-		return nil
-	})
-
-	if err != nil {
-		log.Panic(err)
-	}
-
-	bc := Blockchain{tip, db}
-
-	return &bc
-}
-
-// CreateBlockchain creates a new blockchain DB
-func CreateBlockchain(address string) *Blockchain {
-	if dbExists() {
-		fmt.Println("Blockchain already exists.")
-		os.Exit(1)
-	}
-
-	var tip []byte
-	db, err := bolt.Open(dbFile, 0600, nil)
-	if err != nil {
-		log.Panic(err)
-	}
-
-	err = db.Update(func(tx *bolt.Tx) error {
-		cbtx := NewCoinbaseTX(address, genesisCoinbaseData)
-		genesis := NewGenesisBlock(cbtx)
-
-		b, err := tx.CreateBucket([]byte(blocksBucket))
-		if err != nil {
-			log.Panic(err)
-		}
-
-		err = b.Put(genesis.Hash, genesis.Serialize())
-		if err != nil {
-			log.Panic(err)
-		}
-
-		err = b.Put([]byte("l"), genesis.Hash)
-		if err != nil {
-			log.Panic(err)
-		}
-		tip = genesis.Hash
-
-		return nil
-	})
-
-	if err != nil {
-		log.Panic(err)
-	}
-
-	bc := Blockchain{tip, db}
-
-	return &bc
-}
diff --git a/blockchain_iterator.go b/blockchain_iterator.go
new file mode 100644
index 0000000..305311d
--- /dev/null
+++ b/blockchain_iterator.go
@@ -0,0 +1,34 @@
+package main
+
+import (
+	"log"
+
+	"github.com/boltdb/bolt"
+)
+
+// BlockchainIterator is used to iterate over blockchain blocks
+type BlockchainIterator struct {
+	currentHash []byte
+	db          *bolt.DB
+}
+
+// Next returns next block starting from the tip
+func (i *BlockchainIterator) Next() *Block {
+	var block *Block
+
+	err := i.db.View(func(tx *bolt.Tx) error {
+		b := tx.Bucket([]byte(blocksBucket))
+		encodedBlock := b.Get(i.currentHash)
+		block = DeserializeBlock(encodedBlock)
+
+		return nil
+	})
+
+	if err != nil {
+		log.Panic(err)
+	}
+
+	i.currentHash = block.PrevBlockHash
+
+	return block
+}
diff --git a/cli.go b/cli.go
index 1270c6e..863ffd1 100644
--- a/cli.go
+++ b/cli.go
@@ -5,36 +5,17 @@ import (
 	"fmt"
 	"log"
 	"os"
-	"strconv"
 )
 
 // CLI responsible for processing command line arguments
 type CLI struct{}
 
-func (cli *CLI) createBlockchain(address string) {
-	bc := CreateBlockchain(address)
-	bc.db.Close()
-	fmt.Println("Done!")
-}
-
-func (cli *CLI) getBalance(address string) {
-	bc := NewBlockchain(address)
-	defer bc.db.Close()
-
-	balance := 0
-	UTXOs := bc.FindUTXO(address)
-
-	for _, out := range UTXOs {
-		balance += out.Value
-	}
-
-	fmt.Printf("Balance of '%s': %d\n", address, balance)
-}
-
 func (cli *CLI) printUsage() {
 	fmt.Println("Usage:")
-	fmt.Println("  getbalance -address ADDRESS - Get balance of ADDRESS")
 	fmt.Println("  createblockchain -address ADDRESS - Create a blockchain and send genesis block reward to ADDRESS")
+	fmt.Println("  createwallet - Generates a new key-pair and saves it into the wallet file")
+	fmt.Println("  getbalance -address ADDRESS - Get balance of ADDRESS")
+	fmt.Println("  listaddresses - Lists all addresses from the wallet file")
 	fmt.Println("  printchain - Print all the blocks of the blockchain")
 	fmt.Println("  send -from FROM -to TO -amount AMOUNT - Send AMOUNT of coins from FROM address to TO")
 }
@@ -46,43 +27,14 @@ func (cli *CLI) validateArgs() {
 	}
 }
 
-func (cli *CLI) printChain() {
-	// TODO: Fix this
-	bc := NewBlockchain("")
-	defer bc.db.Close()
-
-	bci := bc.Iterator()
-
-	for {
-		block := bci.Next()
-
-		fmt.Printf("Prev. hash: %x\n", block.PrevBlockHash)
-		fmt.Printf("Hash: %x\n", block.Hash)
-		pow := NewProofOfWork(block)
-		fmt.Printf("PoW: %s\n", strconv.FormatBool(pow.Validate()))
-		fmt.Println()
-
-		if len(block.PrevBlockHash) == 0 {
-			break
-		}
-	}
-}
-
-func (cli *CLI) send(from, to string, amount int) {
-	bc := NewBlockchain(from)
-	defer bc.db.Close()
-
-	tx := NewUTXOTransaction(from, to, amount, bc)
-	bc.MineBlock([]*Transaction{tx})
-	fmt.Println("Success!")
-}
-
 // Run parses command line arguments and processes commands
 func (cli *CLI) Run() {
 	cli.validateArgs()
 
 	getBalanceCmd := flag.NewFlagSet("getbalance", flag.ExitOnError)
 	createBlockchainCmd := flag.NewFlagSet("createblockchain", flag.ExitOnError)
+	createWalletCmd := flag.NewFlagSet("createwallet", flag.ExitOnError)
+	listAddressesCmd := flag.NewFlagSet("listaddresses", flag.ExitOnError)
 	sendCmd := flag.NewFlagSet("send", flag.ExitOnError)
 	printChainCmd := flag.NewFlagSet("printchain", flag.ExitOnError)
 
@@ -103,6 +55,16 @@ func (cli *CLI) Run() {
 		if err != nil {
 			log.Panic(err)
 		}
+	case "createwallet":
+		err := createWalletCmd.Parse(os.Args[2:])
+		if err != nil {
+			log.Panic(err)
+		}
+	case "listaddresses":
+		err := listAddressesCmd.Parse(os.Args[2:])
+		if err != nil {
+			log.Panic(err)
+		}
 	case "printchain":
 		err := printChainCmd.Parse(os.Args[2:])
 		if err != nil {
@@ -134,6 +96,14 @@ func (cli *CLI) Run() {
 		cli.createBlockchain(*createBlockchainAddress)
 	}
 
+	if createWalletCmd.Parsed() {
+		cli.createWallet()
+	}
+
+	if listAddressesCmd.Parsed() {
+		cli.listAddresses()
+	}
+
 	if printChainCmd.Parsed() {
 		cli.printChain()
 	}
diff --git a/cli_createblockchain.go b/cli_createblockchain.go
new file mode 100644
index 0000000..06ff1b1
--- /dev/null
+++ b/cli_createblockchain.go
@@ -0,0 +1,15 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+func (cli *CLI) createBlockchain(address string) {
+	if !ValidateAddress(address) {
+		log.Panic("ERROR: Address is not valid")
+	}
+	bc := CreateBlockchain(address)
+	bc.db.Close()
+	fmt.Println("Done!")
+}
diff --git a/cli_createwallet.go b/cli_createwallet.go
new file mode 100644
index 0000000..b42a142
--- /dev/null
+++ b/cli_createwallet.go
@@ -0,0 +1,11 @@
+package main
+
+import "fmt"
+
+func (cli *CLI) createWallet() {
+	wallets, _ := NewWallets()
+	address := wallets.CreateWallet()
+	wallets.SaveToFile()
+
+	fmt.Printf("Your new address: %s\n", address)
+}
diff --git a/cli_getbalance.go b/cli_getbalance.go
new file mode 100644
index 0000000..27cb55e
--- /dev/null
+++ b/cli_getbalance.go
@@ -0,0 +1,25 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+func (cli *CLI) getBalance(address string) {
+	if !ValidateAddress(address) {
+		log.Panic("ERROR: Address is not valid")
+	}
+	bc := NewBlockchain(address)
+	defer bc.db.Close()
+
+	balance := 0
+	pubKeyHash := Base58Decode([]byte(address))
+	pubKeyHash = pubKeyHash[1 : len(pubKeyHash)-4]
+	UTXOs := bc.FindUTXO(pubKeyHash)
+
+	for _, out := range UTXOs {
+		balance += out.Value
+	}
+
+	fmt.Printf("Balance of '%s': %d\n", address, balance)
+}
diff --git a/cli_listaddress.go b/cli_listaddress.go
new file mode 100644
index 0000000..96fd282
--- /dev/null
+++ b/cli_listaddress.go
@@ -0,0 +1,18 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+func (cli *CLI) listAddresses() {
+	wallets, err := NewWallets()
+	if err != nil {
+		log.Panic(err)
+	}
+	addresses := wallets.GetAddresses()
+
+	for _, address := range addresses {
+		fmt.Println(address)
+	}
+}
diff --git a/cli_printchain.go b/cli_printchain.go
new file mode 100644
index 0000000..cd5c7a0
--- /dev/null
+++ b/cli_printchain.go
@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func (cli *CLI) printChain() {
+	bc := NewBlockchain("")
+	defer bc.db.Close()
+
+	bci := bc.Iterator()
+
+	for {
+		block := bci.Next()
+
+		fmt.Printf("============ Block %x ============\n", block.Hash)
+		fmt.Printf("Prev. block: %x\n", block.PrevBlockHash)
+		pow := NewProofOfWork(block)
+		fmt.Printf("PoW: %s\n\n", strconv.FormatBool(pow.Validate()))
+		for _, tx := range block.Transactions {
+			fmt.Println(tx)
+		}
+		fmt.Printf("\n\n")
+
+		if len(block.PrevBlockHash) == 0 {
+			break
+		}
+	}
+}
diff --git a/cli_send.go b/cli_send.go
new file mode 100644
index 0000000..fb8117c
--- /dev/null
+++ b/cli_send.go
@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+func (cli *CLI) send(from, to string, amount int) {
+	if !ValidateAddress(from) {
+		log.Panic("ERROR: Sender address is not valid")
+	}
+	if !ValidateAddress(to) {
+		log.Panic("ERROR: Recipient address is not valid")
+	}
+
+	bc := NewBlockchain(from)
+	defer bc.db.Close()
+
+	tx := NewUTXOTransaction(from, to, amount, bc)
+	bc.MineBlock([]*Transaction{tx})
+	fmt.Println("Success!")
+}
diff --git a/transaction.go b/transaction.go
index fe82a7b..90950cc 100644
--- a/transaction.go
+++ b/transaction.go
@@ -2,11 +2,17 @@ package main
 
 import (
 	"bytes"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
 	"crypto/sha256"
+	"math/big"
+
 	"encoding/gob"
 	"encoding/hex"
 	"fmt"
 	"log"
+	"strings"
 )
 
 const subsidy = 10
@@ -23,41 +29,145 @@ func (tx Transaction) IsCoinbase() bool {
 	return len(tx.Vin) == 1 && len(tx.Vin[0].Txid) == 0 && tx.Vin[0].Vout == -1
 }
 
-// SetID sets ID of a transaction
-func (tx Transaction) SetID() {
+// Serialize returns a serialized Transaction
+func (tx Transaction) Serialize() []byte {
 	var encoded bytes.Buffer
-	var hash [32]byte
 
 	enc := gob.NewEncoder(&encoded)
 	err := enc.Encode(tx)
 	if err != nil {
 		log.Panic(err)
 	}
-	hash = sha256.Sum256(encoded.Bytes())
-	tx.ID = hash[:]
+
+	return encoded.Bytes()
 }
 
-// TXInput represents a transaction input
-type TXInput struct {
-	Txid      []byte
-	Vout      int
-	ScriptSig string
+// Hash returns the hash of the Transaction
+func (tx *Transaction) Hash() []byte {
+	var hash [32]byte
+
+	txCopy := *tx
+	txCopy.ID = []byte{}
+
+	hash = sha256.Sum256(txCopy.Serialize())
+
+	return hash[:]
 }
 
-// TXOutput represents a transaction output
-type TXOutput struct {
-	Value        int
-	ScriptPubKey string
+// Sign signs each input of a Transaction
+func (tx *Transaction) Sign(privKey ecdsa.PrivateKey, prevTXs map[string]Transaction) {
+	if tx.IsCoinbase() {
+		return
+	}
+
+	for _, vin := range tx.Vin {
+		if prevTXs[hex.EncodeToString(vin.Txid)].ID == nil {
+			log.Panic("ERROR: Previous transaction is not correct")
+		}
+	}
+
+	txCopy := tx.TrimmedCopy()
+
+	for inID, vin := range txCopy.Vin {
+		prevTx := prevTXs[hex.EncodeToString(vin.Txid)]
+		txCopy.Vin[inID].Signature = nil
+		txCopy.Vin[inID].PubKey = prevTx.Vout[vin.Vout].PubKeyHash
+		txCopy.ID = txCopy.Hash()
+		txCopy.Vin[inID].PubKey = nil
+
+		r, s, err := ecdsa.Sign(rand.Reader, &privKey, txCopy.ID)
+		if err != nil {
+			log.Panic(err)
+		}
+		signature := append(r.Bytes(), s.Bytes()...)
+
+		tx.Vin[inID].Signature = signature
+	}
 }
 
-// CanUnlockOutputWith checks whether the address initiated the transaction
-func (in *TXInput) CanUnlockOutputWith(unlockingData string) bool {
-	return in.ScriptSig == unlockingData
+// String returns a human-readable representation of a transaction
+func (tx Transaction) String() string {
+	var lines []string
+
+	lines = append(lines, fmt.Sprintf("--- Transaction %x:", tx.ID))
+
+	for i, input := range tx.Vin {
+
+		lines = append(lines, fmt.Sprintf("     Input %d:", i))
+		lines = append(lines, fmt.Sprintf("       TXID:      %x", input.Txid))
+		lines = append(lines, fmt.Sprintf("       Out:       %d", input.Vout))
+		lines = append(lines, fmt.Sprintf("       Signature: %x", input.Signature))
+		lines = append(lines, fmt.Sprintf("       PubKey:    %x", input.PubKey))
+	}
+
+	for i, output := range tx.Vout {
+		lines = append(lines, fmt.Sprintf("     Output %d:", i))
+		lines = append(lines, fmt.Sprintf("       Value:  %d", output.Value))
+		lines = append(lines, fmt.Sprintf("       Script: %x", output.PubKeyHash))
+	}
+
+	return strings.Join(lines, "\n")
 }
 
-// CanBeUnlockedWith checks if the output can be unlocked with the provided data
-func (out *TXOutput) CanBeUnlockedWith(unlockingData string) bool {
-	return out.ScriptPubKey == unlockingData
+// TrimmedCopy creates a trimmed copy of Transaction to be used in signing
+func (tx *Transaction) TrimmedCopy() Transaction {
+	var inputs []TXInput
+	var outputs []TXOutput
+
+	for _, vin := range tx.Vin {
+		inputs = append(inputs, TXInput{vin.Txid, vin.Vout, nil, nil})
+	}
+
+	for _, vout := range tx.Vout {
+		outputs = append(outputs, TXOutput{vout.Value, vout.PubKeyHash})
+	}
+
+	txCopy := Transaction{tx.ID, inputs, outputs}
+
+	return txCopy
+}
+
+// Verify verifies signatures of Transaction inputs
+func (tx *Transaction) Verify(prevTXs map[string]Transaction) bool {
+	if tx.IsCoinbase() {
+		return true
+	}
+
+	for _, vin := range tx.Vin {
+		if prevTXs[hex.EncodeToString(vin.Txid)].ID == nil {
+			log.Panic("ERROR: Previous transaction is not correct")
+		}
+	}
+
+	txCopy := tx.TrimmedCopy()
+	curve := elliptic.P256()
+
+	for inID, vin := range tx.Vin {
+		prevTx := prevTXs[hex.EncodeToString(vin.Txid)]
+		txCopy.Vin[inID].Signature = nil
+		txCopy.Vin[inID].PubKey = prevTx.Vout[vin.Vout].PubKeyHash
+		txCopy.ID = txCopy.Hash()
+		txCopy.Vin[inID].PubKey = nil
+
+		r := big.Int{}
+		s := big.Int{}
+		sigLen := len(vin.Signature)
+		r.SetBytes(vin.Signature[:(sigLen / 2)])
+		s.SetBytes(vin.Signature[(sigLen / 2):])
+
+		x := big.Int{}
+		y := big.Int{}
+		keyLen := len(vin.PubKey)
+		x.SetBytes(vin.PubKey[:(keyLen / 2)])
+		y.SetBytes(vin.PubKey[(keyLen / 2):])
+
+		rawPubKey := ecdsa.PublicKey{curve, &x, &y}
+		if ecdsa.Verify(&rawPubKey, txCopy.ID, &r, &s) == false {
+			return false
+		}
+	}
+
+	return true
 }
 
 // NewCoinbaseTX creates a new coinbase transaction
@@ -66,10 +176,10 @@ func NewCoinbaseTX(to, data string) *Transaction {
 		data = fmt.Sprintf("Reward to '%s'", to)
 	}
 
-	txin := TXInput{[]byte{}, -1, data}
-	txout := TXOutput{subsidy, to}
-	tx := Transaction{nil, []TXInput{txin}, []TXOutput{txout}}
-	tx.SetID()
+	txin := TXInput{[]byte{}, -1, nil, []byte(data)}
+	txout := NewTXOutput(subsidy, to)
+	tx := Transaction{nil, []TXInput{txin}, []TXOutput{*txout}}
+	tx.ID = tx.Hash()
 
 	return &tx
 }
@@ -79,7 +189,13 @@ func NewUTXOTransaction(from, to string, amount int, bc *Blockchain) *Transactio
 	var inputs []TXInput
 	var outputs []TXOutput
 
-	acc, validOutputs := bc.FindSpendableOutputs(from, amount)
+	wallets, err := NewWallets()
+	if err != nil {
+		log.Panic(err)
+	}
+	wallet := wallets.GetWallet(from)
+	pubKeyHash := HashPubKey(wallet.PublicKey)
+	acc, validOutputs := bc.FindSpendableOutputs(pubKeyHash, amount)
 
 	if acc < amount {
 		log.Panic("ERROR: Not enough funds")
@@ -93,19 +209,20 @@ func NewUTXOTransaction(from, to string, amount int, bc *Blockchain) *Transactio
 		}
 
 		for _, out := range outs {
-			input := TXInput{txID, out, from}
+			input := TXInput{txID, out, nil, wallet.PublicKey}
 			inputs = append(inputs, input)
 		}
 	}
 
 	// Build a list of outputs
-	outputs = append(outputs, TXOutput{amount, to})
+	outputs = append(outputs, *NewTXOutput(amount, to))
 	if acc > amount {
-		outputs = append(outputs, TXOutput{acc - amount, from}) // a change
+		outputs = append(outputs, *NewTXOutput(acc-amount, from)) // a change
 	}
 
 	tx := Transaction{nil, inputs, outputs}
-	tx.SetID()
+	tx.ID = tx.Hash()
+	bc.SignTransaction(&tx, wallet.PrivateKey)
 
 	return &tx
 }
diff --git a/transaction_input.go b/transaction_input.go
new file mode 100644
index 0000000..23beeba
--- /dev/null
+++ b/transaction_input.go
@@ -0,0 +1,18 @@
+package main
+
+import "bytes"
+
+// TXInput represents a transaction input
+type TXInput struct {
+	Txid      []byte
+	Vout      int
+	Signature []byte
+	PubKey    []byte
+}
+
+// UsesKey checks whether the address initiated the transaction
+func (in *TXInput) UsesKey(pubKeyHash []byte) bool {
+	lockingHash := HashPubKey(in.PubKey)
+
+	return bytes.Compare(lockingHash, pubKeyHash) == 0
+}
diff --git a/transaction_output.go b/transaction_output.go
new file mode 100644
index 0000000..4d70d74
--- /dev/null
+++ b/transaction_output.go
@@ -0,0 +1,29 @@
+package main
+
+import "bytes"
+
+// TXOutput represents a transaction output
+type TXOutput struct {
+	Value      int
+	PubKeyHash []byte
+}
+
+// Lock signs the output
+func (out *TXOutput) Lock(address []byte) {
+	pubKeyHash := Base58Decode(address)
+	pubKeyHash = pubKeyHash[1 : len(pubKeyHash)-4]
+	out.PubKeyHash = pubKeyHash
+}
+
+// IsLockedWithKey checks if the output can be used by the owner of the pubkey
+func (out *TXOutput) IsLockedWithKey(pubKeyHash []byte) bool {
+	return bytes.Compare(out.PubKeyHash, pubKeyHash) == 0
+}
+
+// NewTXOutput create a new TXOutput
+func NewTXOutput(value int, address string) *TXOutput {
+	txo := &TXOutput{value, nil}
+	txo.Lock([]byte(address))
+
+	return txo
+}
diff --git a/utils.go b/utils.go
index 7f5e727..aecf919 100644
--- a/utils.go
+++ b/utils.go
@@ -16,3 +16,10 @@ func IntToHex(num int64) []byte {
 
 	return buff.Bytes()
 }
+
+// ReverseBytes reverses a byte array
+func ReverseBytes(data []byte) {
+	for i, j := 0, len(data)-1; i < j; i, j = i+1, j-1 {
+		data[i], data[j] = data[j], data[i]
+	}
+}
diff --git a/wallet.go b/wallet.go
new file mode 100644
index 0000000..31a2258
--- /dev/null
+++ b/wallet.go
@@ -0,0 +1,87 @@
+package main
+
+import (
+	"bytes"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/sha256"
+	"log"
+
+	"golang.org/x/crypto/ripemd160"
+)
+
+const version = byte(0x00)
+const walletFile = "wallet.dat"
+const addressChecksumLen = 4
+
+// Wallet stores private and public keys
+type Wallet struct {
+	PrivateKey ecdsa.PrivateKey
+	PublicKey  []byte
+}
+
+// NewWallet creates and returns a Wallet
+func NewWallet() *Wallet {
+	private, public := newKeyPair()
+	wallet := Wallet{private, public}
+
+	return &wallet
+}
+
+// GetAddress returns wallet address
+func (w Wallet) GetAddress() []byte {
+	pubKeyHash := HashPubKey(w.PublicKey)
+
+	versionedPayload := append([]byte{version}, pubKeyHash...)
+	checksum := checksum(versionedPayload)
+
+	fullPayload := append(versionedPayload, checksum...)
+	address := Base58Encode(fullPayload)
+
+	return address
+}
+
+// HashPubKey hashes public key
+func HashPubKey(pubKey []byte) []byte {
+	publicSHA256 := sha256.Sum256(pubKey)
+
+	RIPEMD160Hasher := ripemd160.New()
+	_, err := RIPEMD160Hasher.Write(publicSHA256[:])
+	if err != nil {
+		log.Panic(err)
+	}
+	publicRIPEMD160 := RIPEMD160Hasher.Sum(nil)
+
+	return publicRIPEMD160
+}
+
+// ValidateAddress check if address if valid
+func ValidateAddress(address string) bool {
+	pubKeyHash := Base58Decode([]byte(address))
+	actualChecksum := pubKeyHash[len(pubKeyHash)-addressChecksumLen:]
+	version := pubKeyHash[0]
+	pubKeyHash = pubKeyHash[1 : len(pubKeyHash)-addressChecksumLen]
+	targetChecksum := checksum(append([]byte{version}, pubKeyHash...))
+
+	return bytes.Compare(actualChecksum, targetChecksum) == 0
+}
+
+// Checksum generates a checksum for a public key
+func checksum(payload []byte) []byte {
+	firstSHA := sha256.Sum256(payload)
+	secondSHA := sha256.Sum256(firstSHA[:])
+
+	return secondSHA[:addressChecksumLen]
+}
+
+func newKeyPair() (ecdsa.PrivateKey, []byte) {
+	curve := elliptic.P256()
+	private, err := ecdsa.GenerateKey(curve, rand.Reader)
+	if err != nil {
+		log.Panic(err)
+	}
+	pubKey := append(private.PublicKey.X.Bytes(), private.PublicKey.Y.Bytes()...)
+
+	return *private, pubKey
+}
diff --git a/wallets.go b/wallets.go
new file mode 100644
index 0000000..e5b2134
--- /dev/null
+++ b/wallets.go
@@ -0,0 +1,94 @@
+package main
+
+import (
+	"bytes"
+	"crypto/elliptic"
+	"encoding/gob"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+)
+
+// Wallets stores a collection of wallets
+type Wallets struct {
+	Wallets map[string]*Wallet
+}
+
+// NewWallets creates Wallets and fills it from a file if it exists
+func NewWallets() (*Wallets, error) {
+	wallets := Wallets{}
+	wallets.Wallets = make(map[string]*Wallet)
+
+	err := wallets.LoadFromFile()
+
+	return &wallets, err
+}
+
+// CreateWallet adds a Wallet to Wallets
+func (ws *Wallets) CreateWallet() string {
+	wallet := NewWallet()
+	address := fmt.Sprintf("%s", wallet.GetAddress())
+
+	ws.Wallets[address] = wallet
+
+	return address
+}
+
+// GetAddresses returns an array of addresses stored in the wallet file
+func (ws *Wallets) GetAddresses() []string {
+	var addresses []string
+
+	for address := range ws.Wallets {
+		addresses = append(addresses, address)
+	}
+
+	return addresses
+}
+
+// GetWallet returns a Wallet by its address
+func (ws Wallets) GetWallet(address string) Wallet {
+	return *ws.Wallets[address]
+}
+
+// LoadFromFile loads wallets from the file
+func (ws *Wallets) LoadFromFile() error {
+	if _, err := os.Stat(walletFile); os.IsNotExist(err) {
+		return err
+	}
+
+	fileContent, err := ioutil.ReadFile(walletFile)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	var wallets Wallets
+	gob.Register(elliptic.P256())
+	decoder := gob.NewDecoder(bytes.NewReader(fileContent))
+	err = decoder.Decode(&wallets)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	ws.Wallets = wallets.Wallets
+
+	return nil
+}
+
+// SaveToFile saves wallets to a file
+func (ws Wallets) SaveToFile() {
+	var content bytes.Buffer
+
+	gob.Register(elliptic.P256())
+
+	encoder := gob.NewEncoder(&content)
+	err := encoder.Encode(ws)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	err = ioutil.WriteFile(walletFile, content.Bytes(), 0644)
+	if err != nil {
+		log.Panic(err)
+	}
+}