Online AES encryption/decryption tool with ECB, CBC, CTR, and GCM modes. Supports 128, 192, and 256-bit keys. Built for secure, real-world use.
Advanced Encryption Standard (AES)
is a fast and secure symmetric encryption algorithm widely used to
protect sensitive data. It supports 128-bit, 192-bit, and 256-bit keys
and is used in databases, file encryption, APIs, and secure communications.
This tool supports multiple cipher modes — ECB, CBC, CTR, and GCM —
with AES-GCM
being the recommended choice as it provides both encryption and integrity.
Learn more in this Java AES implementation guide.
Symmetric Cipher Same key for both encryption and decryption — fast for bulk data
128 / 192 / 256-bit Keys Flexible key sizes to match your security and performance needs
AES Encryption
⚠️ Plain-text secret keys are weak. Choose Hex/Base64 or PBKDF2-derived keys
for stronger security.
AES Decryption
Common AES Encryption & Decryption Errors (and Fixes)
Wrong AES Mode Selected
Using insecure or incorrect AES modes is the most common cause of weak encryption.
AES-ECB leaks patterns and should never be used for real data —
identical plaintext blocks produce identical ciphertext, revealing structure.
Fix: Use AES-GCM for authenticated encryption, or AES-CBC with a secure MAC if GCM is unavailable.
Invalid IV Length
AES requires a 16-byte (128-bit) IV for block modes like CBC.
Using an incorrect IV size causes decryption failures or weak encryption.
Fix: Always generate a random 16-byte IV for each encryption. Use the Generate button in the tool above.
Authentication Tag Verification Failed (AES-GCM)
This error occurs when ciphertext or associated data is modified, or when the wrong
key or IV is used during decryption.
Fix: Ensure the same key, IV, and associated data are used for both encryption and decryption.
Padding Errors (PKCS5Padding)
Padding errors happen when decrypting data with mismatched padding or corrupted
ciphertext.
Fix: Ensure the same padding scheme is used on both sides. Switch to AES-GCM to avoid padding-based modes entirely.
Secret Key Format
Secret Key must be provided in one of these formats: Hex / Base64 / Plain Text.
Key length must match the selected key size:
128-bit → 16 bytes (e.g. 32 hex characters)
192-bit → 24 bytes
256-bit → 32 bytes
Example: 32 hex chars = 16 bytes (AES-128)
Using a plain-text password directly as an encryption key is not recommended.
Human-readable passwords usually have low entropy and are vulnerable to brute-force and dictionary attacks.
For stronger security, derive a key from your password using PBKDF2 — this generates a cryptographically strong 32-byte key using salting and multiple iterations.
Use the PBKDF2 Hashing Online Tool to generate one.
IV Format & Security Concerns
IV can be Hex / Base64 / Plain Text.
IV must be exactly 16 bytes (128-bit):
32 hex characters
or a Base64 string that decodes to 16 bytes
or 16 plain text bytes
IV is optional in this tool for convenience, but using a random IV is strongly recommended.
If IV is missing, many libraries default to 00000000000000000000000000000000 — making encryption deterministic and able to reveal patterns.
Without a random IV, identical plaintext encrypted with the same key produces identical ciphertext — this leaks information and weakens security.
Best practice: always use a random IV for CBC/CFB/GCM modes and never reuse an IV with the same key.
Prefer AES-GCM for modern applications — it provides encryption and authentication in one operation
Never use AES-ECB for real data — it reveals patterns in identical plaintext blocks
Always use a random, unique IV for every encryption operation
Never reuse encryption keys or IVs across different systems or purposes
Use AES only for data encryption — not for password storage; use bcrypt, scrypt, or Argon2 instead
Security note: AES-GCM provides confidentiality and integrity in one pass.
CBC and CTR modes require additional authentication (MAC) to prevent tampering.
Symmetric Key Algorithm
The same secret key is used for both encryption and decryption — making AES fast and efficient for bulk data.
Block Cipher
AES operates on fixed-size blocks of 128 bits. Data is divided into 16-byte chunks before encryption.
Flexible Key Sizes
Supports 128-bit, 192-bit, and 256-bit encryption. AES-256 is trusted by governments and enterprises for high-security data.
Industry Standard
Widely used in databases, file encryption, APIs, TLS/SSL, and cloud security worldwide.
AES Encryption Concepts
To encrypt data, enter the plain text or password and choose an appropriate
AES mode of operation.
Each mode offers different security and performance characteristics.
Supported AES Modes of Operation
Mode
IV Required
Padding
Authentication
Status
ECB
No
PKCS5
No
Not Recommended
CBC
Yes (16 bytes)
PKCS5
No (add MAC)
Acceptable
CTR
Yes (16 bytes)
None
No (add MAC)
Good
GCM
Yes (16 bytes)
None
Yes (built-in)
Recommended
ECB (Electronic Codebook) does not use an IV and produces identical ciphertext
for identical plaintext blocks, making it insecure for real-world usage.
CBC (Cipher Block Chaining) uses an Initialization Vector (IV) to randomize output
— more secure than ECB but does not provide authentication.
CTR (Counter Mode) turns AES into a stream cipher and allows parallel processing,
making it suitable for high-performance systems.
GCM (Galois/Counter Mode) provides authenticated encryption,
ensuring confidentiality and integrity — the recommended mode for modern applications and APIs.
Padding
Block-based modes like ECB and CBC require
padding such as
PKCS5Padding to align data to the 16-byte AES block size.
Streaming modes like AES-GCM do not require padding.
AES Key Size and IV
AES always uses a 128-bit block size.
When an IV is required, it must be 16 bytes (128 bits) long.
Secret key sizes must be 16, 24, or 32 bytes for AES-128, AES-192, and AES-256
respectively.
Encrypted output is
Base64
encoded
by default, with an option to export ciphertext in HEX format.
AES vs RSA vs DES
AES is a symmetric encryption algorithm designed for speed and
efficiency.
RSA is an asymmetric algorithm mainly used for secure key
exchange and digital signatures,
while DES
is an outdated symmetric cipher and is no longer
considered secure.
Feature
AES
RSA
DES
Encryption Type
Symmetric
Asymmetric
Symmetric
Performance
Very fast
Slow
Fast but insecure
Key Size
128 / 192 / 256 bits
2048+ bits
56 bits
Security Status
Highly secure
Secure
Broken / deprecated
Typical Usage
Encrypting data
Key exchange
Legacy systems
In practice, AES is often used together with
RSA
encryption,
where RSA secures the AES secret key and AES encrypts the actual data.
When NOT to Use AES
Password Storage:
AES is reversible encryption and should never be used to store passwords.
Use bcrypt, scrypt, or Argon2 instead.
Unauthenticated Encryption:
Using ECB or CBC without integrity protection can allow data tampering.
Prefer AES-GCM or MAC-based solutions like
Poly1305.
Poor Key Management:
Hardcoded keys, reused IVs, or weak randomness can compromise AES security entirely.
Public-Key Requirements:
AES is not suitable for digital signatures or secure key exchange.
Use RSA or elliptic-curve cryptography for these use cases.
Applications of AES Encryption
Data Protection: Encrypting sensitive files and database
fields.
Secure Communication: HTTPS, SSL/TLS, and API payload
encryption.
Authenticated Encryption:
Used with MACs such as
Poly1305
to ensure integrity.
Yes. AES is considered highly secure when used with strong keys and modern modes like AES-GCM.
AES-256 is widely trusted by governments and enterprises.
No. Passwords should be hashed using slow, memory-hard algorithms such as
bcrypt, scrypt, or Argon2 instead of reversible encryption.
AES-GCM is the recommended choice as it provides encryption and authentication
in a single, efficient operation.
There are no practical attacks against properly implemented AES.
Most vulnerabilities arise from incorrect usage, weak keys, or poor key management.
AES-128 uses a 128-bit key (16 bytes) and performs 10 rounds of encryption.
AES-256 uses a 256-bit key (32 bytes) and performs 14 rounds — providing a larger security margin at a small performance cost.
Both are considered secure; AES-256 is preferred for high-security and long-lived data.
Yes. AES-GCM requires a nonce (IV) — typically 12 bytes (96 bits) for optimal performance, though this tool uses 16 bytes to stay consistent with other modes.
The IV must be unique for every encryption with the same key.
Reusing a nonce in GCM mode completely breaks its authentication guarantee.
Support This Free Tool!
I build these tools to give you fast, secure, privacy-friendly utilities—free
and
signup-free.
Buying me a coffee helps keep the project running and
supports
new features.
