diff --git a/apps/cli/blob.py b/apps/cli/blob.py
index d2bf390..6041050 100644
--- a/apps/cli/blob.py
+++ b/apps/cli/blob.py
@@ -1,3 +1,4 @@
+import re
 from hashlib import sha256
 from binascii import hexlify, unhexlify
 from cryptography.hazmat.primitives.ciphers.aead import AESGCM
@@ -8,6 +9,9 @@ from apps.cli import SUPPORTED_HASH_FUNCTIONS, SUPPORTED_CIPHERS
 
 class Blob:
     def __init__(self, data, cipher, hash_function):
+        if type(data) is not str or re.search(r'^[0-9A-Fa-f]+$', data) is None:
+            raise ValueError("Non-Hex character found in txid.")
+
         self.data = data
         self.cipher = cipher
         self.hash_function = hash_function
@@ -23,6 +27,12 @@ class Blob:
                                                                                        SUPPORTED_CIPHERS))
 
     def encrypt(self, tx_id):
+        if len(tx_id) != 64:
+            raise ValueError("txid does not matches the expected size (32-byte / 64 hex chars).")
+
+        elif re.search(r'^[0-9A-Fa-f]+$', tx_id) is None:
+            raise ValueError("Non-Hex character found in txid.")
+
         # Transaction to be encrypted
         # FIXME: The blob data should contain more things that just the transaction. Leaving like this for now.
         tx = unhexlify(self.data)
diff --git a/test/unit/test_blob.py b/test/unit/test_blob.py
new file mode 100644
index 0000000..fc95450
--- /dev/null
+++ b/test/unit/test_blob.py
@@ -0,0 +1,94 @@
+from os import urandom
+
+from pisa import logging
+from apps.cli.blob import Blob
+from pisa.conf import SUPPORTED_CIPHERS, SUPPORTED_HASH_FUNCTIONS
+
+
+def test_init_blob():
+    data = urandom(64).hex()
+
+    # Fixed (valid) hash function, try different valid ciphers
+    hash_function = SUPPORTED_HASH_FUNCTIONS[0]
+    for cipher in SUPPORTED_CIPHERS:
+        cipher_cases = [cipher, cipher.lower(), cipher.capitalize()]
+
+        for case in cipher_cases:
+            blob = Blob(data, case, hash_function)
+            assert(blob.data == data and blob.cipher == case and blob.hash_function == hash_function)
+
+    # Fixed (valid) cipher, try different valid hash functions
+    cipher = SUPPORTED_CIPHERS[0]
+    for hash_function in SUPPORTED_HASH_FUNCTIONS:
+        hash_function_cases = [hash_function, hash_function.lower(), hash_function.capitalize()]
+
+        for case in hash_function_cases:
+            blob = Blob(data, cipher, case)
+            assert(blob.data == data and blob.cipher == cipher and blob.hash_function == case)
+
+    # Invalid data
+    data = urandom(64)
+    cipher = SUPPORTED_CIPHERS[0]
+    hash_function = SUPPORTED_HASH_FUNCTIONS[0]
+
+    try:
+        Blob(data, cipher, hash_function)
+        assert False, "Able to create blob with wrong data"
+
+    except ValueError:
+        assert True
+
+    # Invalid cipher
+    data = urandom(64).hex()
+    cipher = "A" * 10
+    hash_function = SUPPORTED_HASH_FUNCTIONS[0]
+
+    try:
+        Blob(data, cipher, hash_function)
+        assert False, "Able to create blob with wrong data"
+
+    except ValueError:
+        assert True
+
+    # Invalid hash function
+    data = urandom(64).hex()
+    cipher = SUPPORTED_CIPHERS[0]
+    hash_function = "A" * 10
+
+    try:
+        Blob(data, cipher, hash_function)
+        assert(False, "Able to create blob with wrong data")
+
+    except ValueError:
+        assert True
+
+
+def test_encrypt():
+    # Valid data, valid key
+    data = urandom(64).hex()
+    blob = Blob(data, SUPPORTED_CIPHERS[0], SUPPORTED_HASH_FUNCTIONS[0])
+    key = urandom(32).hex()
+
+    encrypted_blob = blob.encrypt(key)
+
+    # Invalid key (note that encrypt cannot be called with invalid data since that's checked when the Blob is created)
+    invalid_key = urandom(32)
+
+    try:
+        blob.encrypt(invalid_key)
+        assert (False, "Able to create encrypt with invalid key")
+
+    except ValueError:
+        assert True
+
+    # Check that two encryptions of the same data have the same result
+    encrypted_blob2 = blob.encrypt(key)
+
+    assert(encrypted_blob == encrypted_blob2 and id(encrypted_blob) != id(encrypted_blob2))
+
+
+logging.getLogger().disabled = True
+
+test_init_blob()
+test_encrypt()
+