update string encryption/decryption

Author: spencer-xyz

README.md

@@ -223,7 +223,30 @@ int_cipher_text, signature = build_input_text(plaintext, user_aes_key, sender, c
 - `int_cipher_text`: The integer representation of the ciphertext.
 - `signature`: The generated signature.
 
-### 8. `generate_rsa_keypair()`
+### 8. `build_string_input_text(plaintext, user_aes_key, sender, contract, func_sig, signing_key)`
+
+**Purpose:** Builds input text by encrypting the plaintext and signing it.
+
+**Usage:**
+
+```python
+int_cipher_text, signature = build_string_input_text(plaintext, user_aes_key, sender, contract, func_sig, signing_key)
+```
+
+**Parameters:**
+
+- `plaintext`: The plaintext message.
+- `user_aes_key`: The user's AES key.
+- `sender`: The sender's address.
+- `contract`: The contract address.
+- `func_sig`: The function signature.
+- `signing_key`: The private key used for signing.
+
+**Returns:**
+
+- `input_text`: A dictionary of the form { "ciphertext": { "value": int[] }, "signature": bytes[] }
+
+### 9. `generate_rsa_keypair()`
 
 **Purpose:** Generates an RSA key pair.
 
@@ -238,7 +261,7 @@ private_key_bytes, public_key_bytes = generate_rsa_keypair()
 - `private_key_bytes`: The serialized private key.
 - `public_key_bytes`: The serialized public key.
 
-### 9. `encrypt_rsa(public_key_bytes, plaintext)`
+### 10. `encrypt_rsa(public_key_bytes, plaintext)`
 
 **Purpose:** Encrypts plaintext using RSA encryption with a provided public key.
 
@@ -257,7 +280,7 @@ ciphertext = encrypt_rsa(public_key_bytes, plaintext)
 
 - `ciphertext`: The encrypted message.
 
-### 10. `decrypt_rsa(private_key_bytes, ciphertext)`
+### 11. `decrypt_rsa(private_key_bytes, ciphertext)`
 
 **Purpose:** Decrypts ciphertext using RSA decryption with a provided private key.
 
@@ -276,7 +299,7 @@ plaintext = decrypt_rsa(private_key_bytes, ciphertext)
 
 - `plaintext`: The decrypted message.
 
-### 11. `keccak256(data)`
+### 12. `keccak256(data)`
 
 **Purpose:** Computes the Keccak-256 hash of the provided data.
 
@@ -294,7 +317,7 @@ hash_value = keccak256(data)
 
 - `hash_value`: The computed hash.
 
-### 12. `get_func_sig(function_signature)`
+### 13. `get_func_sig(function_signature)`
 
 **Purpose:** Computes the function signature hash using Keccak-256.
 
@@ -312,7 +335,7 @@ func_sig_hash = get_func_sig(function_signature)
 
 - `func_sig_hash`: The first 4 bytes of the computed hash.
 
-### 13. `decrypt_uint(ciphertext, user_key)`
+### 14. `decrypt_uint(ciphertext, user_key)`
 
 **Purpose:** Decrypts a value stored in a contract using a user key
 
@@ -331,7 +354,7 @@ plaintext = decrypt_uint(ciphertext, user_key)
 
 - `result`: The decrypted value.
 
-### 14. `decrypt_string(ciphertext, user_key)`
+### 15. `decrypt_string(ciphertext, user_key)`
 
 **Purpose:** Decrypts a value stored in a contract using a user key
 
@@ -343,7 +366,7 @@ plaintext = decrypt_string(ciphertext, user_key)
 
 **Parameters:**
 
-- `ciphertext`: The value to be decrypted.
+- `ciphertext`: A dictionary of the form { "value": int[] } where each cell holds up to 8 characters (padded at the end with zeroes) encrypted
 - `userKey`: The user's AES key.
 
 **Returns:**

coti/crypto_utils.py

@@ -1,6 +1,3 @@
-import binascii
-from array import array
-
 from Crypto.Cipher import AES
 from Crypto.Hash import keccak
 from Crypto.Random import get_random_bytes
@@ -9,6 +6,7 @@
 from cryptography.hazmat.primitives.asymmetric import padding
 from cryptography.hazmat.primitives.asymmetric import rsa
 from eth_keys import keys
+from math import ceil
 
 block_size = AES.block_size
 address_size = 20
@@ -24,6 +22,7 @@ def encrypt(key, plaintext):
 
     # Ensure key size is 128 bits (16 bytes)
     if len(key) != block_size:
+        print(len(key), block_size)
         raise ValueError("Key size must be 128 bits.")
 
     # Create a new AES cipher block using the provided key
@@ -126,14 +125,34 @@ def build_input_text(plaintext, user_aes_key, sender, contract, func_sig, signin
 
 
 def build_string_input_text(plaintext, user_aes_key, sender, contract, func_sig, signing_key):
-    encoded_plaintext = array('B', plaintext.encode('utf-8'))
-    encrypted_str = [{'ciphertext': 0, 'signature': b''} for _ in range(len(encoded_plaintext))]
-    for i in range(len(encoded_plaintext)):
-        ct_int, signature = build_input_text(int(encoded_plaintext[i]), user_aes_key, sender, contract,
-                                             func_sig, signing_key)
-        encrypted_str[i] = {'ciphertext': ct_int, 'signature': signature}
+    input_text = {
+        'ciphertext': {
+            'value': []
+        },
+        'signature': []
+    }
+
+    encoded_plaintext = bytearray(list(plaintext.encode('utf-8')))
+
+    for i in range(ceil(len(encoded_plaintext) / 8)):
+        start_idx = i * 8
+        end_idx = min(start_idx + 8, len(encoded_plaintext))
+
+        byte_arr = encoded_plaintext[start_idx:end_idx] + bytearray(8 - (end_idx - start_idx))
+
+        ct_int, sig = build_input_text(
+            int.from_bytes(byte_arr, 'big'),
+            user_aes_key,
+            sender,
+            contract,
+            func_sig,
+            signing_key
+        )
 
-    return encrypted_str
+        input_text['ciphertext']['value'].append(ct_int)
+        input_text['signature'].append(sig)
+    
+    return input_text
 
 
 def decrypt_uint(ciphertext, user_key):
@@ -154,18 +173,19 @@ def decrypt_uint(ciphertext, user_key):
 
 
 def decrypt_string(ciphertext, user_key):
-    string_from_input_tx = ""
-    for input_text_from_tx in ciphertext:
-        decrypted_input_from_tx = decrypt_uint(input_text_from_tx, user_key)
-        byte_length = (decrypted_input_from_tx.bit_length() + 7) // 8  # calculate the byte length
+    decrypted_string = ""
+
+    for value in ciphertext['value']:
+        decrypted = decrypt_uint(value, user_key)
+        byte_length = (decrypted.bit_length() + 7) // 8  # calculate the byte length
 
         # Convert the integer to bytes
-        decrypted_bytes = decrypted_input_from_tx.to_bytes(byte_length, byteorder='big')
+        decrypted_bytes = decrypted.to_bytes(byte_length, byteorder='big')
 
         # Decode the bytes to a string
-        string_from_input_tx += decrypted_bytes.decode('utf-8')
-
-    return string_from_input_tx
+        decrypted_string += decrypted_bytes.decode('utf-8')
+    
+    return decrypted_string.strip('\0')
 
 
 def generate_rsa_keypair():