AES uses a key schedule to expand a short key into a number of separate round keys. The three AES variants have a different number of rounds. Each variant requires a separate 128-bit round key for each round plus one more. The key schedule produces the needed round keys from the initial key. Mar 05, 2015  Using Key/SecureKey. Now, let's show a simple example of creating an encrypted standard string with the use of a key. AES encryption only supports 128-bit (16 bytes), 192-bit (24 bytes) or 256-bit key (32 bytes) lengths, so we'll need to create or generate an appropriate key. RandomKeygen is a free mobile-friendly tool that offers randomly generated keys and passwords you can use to secure any application, service or device. KEY RandomKeygen - The Secure Password & Keygen Generator.

1. Generate 256 Bit Key
2. C Generate 256 Bit Aes Key Size

AES uses a key schedule to expand a short key into a number of separate round keys. The three AES variants have a different number of rounds. Each variant requires a separate 128-bit round key for each round plus one more.^{[note 1]} The key schedule produces the needed round keys from the initial key.

Round constants[edit]

The round constant rcon_i for round i of the key expansion is the 32-bit word:

where rc_i is an eight-bit value defined as:

where ${\displaystyle \oplus }$ is the bitwise XOR operator and constants such as 00₁₆ and 1B₁₆ are given in hexadecimal. Equivalently:

Generate 256 Bit Key

${\displaystyle r{c}_i=x^{i-1}}$

where the bits of rc_i are treated as the coefficients of an element of the finite field${\displaystyle \mathrm{G}\mathrm{F}(2)[\mathrm{x}]/({\mathrm{x}}^8+{\mathrm{x}}^4+{\mathrm{x}}^3+\mathrm{x}+1)}$, so that e.g. Driver easy key generator 5.6.2. ${\displaystyle r{c}_{10}={36}_{16}={00110110}_2}$ represents the polynomial ${\displaystyle x^5+x^4+x^2+x}$.

C Generate 256 Bit Aes Key Size

AES uses up to rcon₁₀ for AES-128 (as 11 round keys are needed), up to rcon₈ for AES-192, and up to rcon₇ for AES-256.^{[note 2]}

The key schedule[edit]

Define:

• N as the length of the key in 32-bit words: 4 words for AES-128, 6 words for AES-192, and 8 words for AES-256
• K₀, K₁, .. K_N-1 as the 32-bit words of the original key
• R as the number of round keys needed: 11 round keys for AES-128, 13 keys for AES-192, and 15 keys for AES-256^{[note 3]}
• W₀, W₁, .. W_4R-1 as the 32-bit words of the expanded key^{[note 4]}

Also define RotWord as a one-byte left circular shift:

and SubWord as an application of the AES S-box to each of the four bytes of the word:

Then for ${\displaystyle i=0\dots 4R-1}$:

Notes[edit]

1. ^Non-AES Rijndael variants require up to 256 bits of expanded key per round
2. ^The Rijndael variants with larger block sizes use more of these constants, up to rcon₂₉ for Rijndael with 128-bit keys and 256 bit blocks (needs 15 round keys of each 256 bit, which means 30 full rounds of key expansion, which means 29 calls to the key schedule core using the round constants). The remaining constants for i ≥ 11 are: 6C, D8, AB, 4D, 9A, 2F, 5E, BC, 63, C6, 97, 35, 6A, D4, B3, 7D, FA, EF and C5
3. ^Other Rijndael variants require max(N, B) + 7 round keys, where B is the block size in words
4. ^Other Rijndael variants require BR words of expanded key, where B is the block size in words

References[edit]

• FIPS PUB 197: the official AES standard (PDF file)

External links[edit]

• schematic view of the key schedule for 128 and 256 bit keysfor 160-bit keys on Cryptography Stack Exchange

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Implementation for php 7.x was added

As you see this implementation is using openssl instead of mcrypt and the result of the encryption/decryption is not compatible with each other.
The mcrypt function will be deprecated feature in PHP 7.1.x

What is AES encryption?

It is a webtool to encrypt and decrypt text using AES encryption algorithm. You can chose 128, 192 or 256-bit long key size for encryption and decryption. The result of the process is downloadable in a text file.

How to use AES encryption?

If you want to encrypt a text put it in the white textarea above, set the key of the encryption then push the Encrypt button.
The result of the encryption will appear in base64 encoded to prevent character encoding problems.
If you want to decrypt a text be sure it is in base64 encoded and is encrypted with AES algorithm!
Put the encrypted text in the white textarea, set the key and push the Decrypt button.

When is helpful to use AES encryption?

When you want to encrypt a confidential text into a decryptable format, for example when you need to send sensitive data in e-mail.
The decryption of the encrypted text it is possible only if you know the right password.

What is AES encryption?

AES (acronym of Advanced Encryption Standard) is a symmetric encryption algorithm.
The algorithm was developed by two Belgian cryptographer Joan Daemen and Vincent Rijmen.
AES was designed to be efficient in both hardware and software, and supports a block length of 128 bits and key lengths of 128, 192, and 256 bits.

How secure is AES encryption algorithm?

AES encryption is used by U.S. for securing sensitive but unclassified material, so we can say it is enough secure.