ch04: Fix 'key-to-address-ecc-example'

The 'pybitcointools' library is deprecated. Vitalik mentions using the
fork from 'primal100'. This updates the code sample which is currently
broken, to use the Python package for that fork.

Runs all good now.

code/key-to-address-ecc-example.py

@@ -1,18 +1,18 @@
 from __future__ import print_function
-import bitcoin
+import cryptos
 
 # Generate a random private key
 valid_private_key = False
 while not valid_private_key:
-    private_key = bitcoin.random_key()
-    decoded_private_key = bitcoin.decode_privkey(private_key, 'hex')
-    valid_private_key = 0 < decoded_private_key < bitcoin.N
+    private_key = cryptos.random_key()
+    decoded_private_key = cryptos.decode_privkey(private_key, 'hex')
+    valid_private_key = 0 < decoded_private_key < cryptos.N
 
 print("Private Key (hex) is: ", private_key)
 print("Private Key (decimal) is: ", decoded_private_key)
 
 # Convert private key to WIF format
-wif_encoded_private_key = bitcoin.encode_privkey(decoded_private_key, 'wif')
+wif_encoded_private_key = cryptos.encode_privkey(decoded_private_key, 'wif')
 print("Private Key (WIF) is: ", wif_encoded_private_key)
 
 # Add suffix "01" to indicate a compressed private key
@@ -20,27 +20,27 @@ compressed_private_key = private_key + '01'
 print("Private Key Compressed (hex) is: ", compressed_private_key)
 
 # Generate a WIF format from the compressed private key (WIF-compressed)
-wif_compressed_private_key = bitcoin.encode_privkey(
-    bitcoin.decode_privkey(compressed_private_key, 'hex'), 'wif')
+wif_compressed_private_key = cryptos.encode_privkey(
+    cryptos.decode_privkey(compressed_private_key, 'hex'), 'wif')
 print("Private Key (WIF-Compressed) is: ", wif_compressed_private_key)
 
 # Multiply the EC generator point G with the private key to get a public key point
-public_key = bitcoin.fast_multiply(bitcoin.G, decoded_private_key)
+public_key = cryptos.fast_multiply(cryptos.G, decoded_private_key)
 print("Public Key (x,y) coordinates is:", public_key)
 
 # Encode as hex, prefix 04
-hex_encoded_public_key = bitcoin.encode_pubkey(public_key, 'hex')
+hex_encoded_public_key = cryptos.encode_pubkey(public_key, 'hex')
 print("Public Key (hex) is:", hex_encoded_public_key)
 
 # Compress public key, adjust prefix depending on whether y is even or odd
 (public_key_x, public_key_y) = public_key
 compressed_prefix = '02' if (public_key_y % 2) == 0 else '03'
-hex_compressed_public_key = compressed_prefix + (bitcoin.encode(public_key_x, 16).zfill(64))
+hex_compressed_public_key = compressed_prefix + (cryptos.encode(public_key_x, 16).zfill(64))
 print("Compressed Public Key (hex) is:", hex_compressed_public_key)
 
 # Generate bitcoin address from public key
-print("Bitcoin Address (b58check) is:", bitcoin.pubkey_to_address(public_key))
+print("Bitcoin Address (b58check) is:", cryptos.pubkey_to_address(public_key))
 
 # Generate compressed bitcoin address from compressed public key
 print("Compressed Bitcoin Address (b58check) is:",
-      bitcoin.pubkey_to_address(hex_compressed_public_key))
+      cryptos.pubkey_to_address(hex_compressed_public_key))