AES Encryption and Decryption Online

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 commonly used in databases, file encryption, APIs, and secure communications.

This online tool allows you to encrypt and decrypt text using AES in multiple modes such as ECB, CBC, CTR, and GCM. AES-GCM is the recommended choice as it provides both encryption and integrity with better performance. Learn more about AES here.

We do not store, log, or transmit any data or secret keys. It is intended for educational and personal testing. Do not use online tools for protecting real production secrets.

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.

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.

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 and avoid padding-based modes when possible by switching to AES-GCM.

Secret Key Format

• Secret Key must be provided in one of these formats: Hex / Base64 / Plain Text.
• Key length must match selected key size:
  • 128-bit → 16 bytes
  • 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, it is recommended to derive a key from your password using PBKDF2. This approach generates a cryptographically strong 32-byte key using salting and multiple iterations.

You can generate a secure key using the following tool: PBKDF2 Hashing Online Tool

IV Format

• IV can be Hex / Base64 / Plain Text.
• IV must be exactly 16 bytes (128-bit):
  • 32 hex characters
  • or Base64 string that decodes to 16 bytes
  • or 16 plain text bytes

Security Concerns (IV)

• IV is optional in this tool for convenience, but using a random IV is strongly recommended.
• If IV is missing, many libraries use a default IV of 00000000000000000000000000000000. This makes encryption deterministic and can 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 IV with the same key.

You can analyze insecure AES usage using our Crypto Safety Validator.

Secure Usage Guidelines for AES

• Prefer AES-GCM for modern applications
• Never use AES-ECB for real data
• Use a random IV for every encryption
• Do not reuse encryption keys across systems
• Use AES only for data encryption, not passwords

Security note: AES-GCM provides confidentiality and integrity. CBC and CTR modes require additional authentication (MAC) to prevent tampering.

MAC Generators
• HMAC Generator
• PolyMac1305 Generator

Key Features of AES Encryption

• Symmetric Key Algorithm: The same secret key is used for both encryption and decryption.
• Block Cipher: AES operates on fixed-size blocks of 128 bits.
• Key Sizes: Supports 128-bit, 192-bit, and 256-bit encryption.
• Industry Standard: Widely used in databases, file encryption, APIs, TLS/SSL, and cloud security.

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

• 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. It is 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. AES-GCM is 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.

Security Best Practices

• Prefer AES-GCM over ECB or CBC for real-world applications.
• Always use a random and unique IV for each encryption.
• Never reuse encryption keys across different systems or purposes.
• Do not use AES for password storage. Instead, use bcrypt, scrypt, or Argon2.

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.

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.

Frequently Asked Questions (FAQ)

Is AES encryption secure?

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.

Should I use AES to store passwords?

No. Passwords should be hashed using slow, memory-hard algorithms such as bcrypt, scrypt, or Argon2 instead of reversible encryption.

What is the best AES mode to use?

AES-GCM is the recommended choice as it provides encryption and authentication in a single, efficient operation.

Can AES be cracked?

There are no practical attacks against properly implemented AES. Most vulnerabilities arise from incorrect usage, weak keys, or poor key management.

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