Invalid Crypto Padding
The term “Invalid Crypto Padding” refers to an issue where the padding used in cryptographic algorithms is incorrect or does not conform to the expected pattern. Cryptographic padding is a technique used to fill the plaintext blocks to the required size before encryption or after decryption.
Explanation
When performing encryption or decryption using block ciphers, such as AES (Advanced Encryption Standard), the data being processed is divided into fixed-sized blocks. However, the data may not perfectly align with these blocks, so padding is added to fill the remaining space.
There are various padding schemes available, such as PKCS#5 (or PKCS#7) padding, Zero padding, ANSI X.923 padding, etc. The padding scheme used during encryption needs to match the padding scheme used during decryption; otherwise, the process fails with an “Invalid Crypto Padding” error.
Example:
Let’s consider an example using PKCS#5 padding:
// Encryption
Plaintext: "Hello"
Block size: 8 bytes
Plaintext in hex: 48 65 6C 6C 6F
Padding required: 3 bytes
Padded plaintext: 48 65 6C 6C 6F 05 05 05
// Decryption
Ciphertext: 48 65 6C 6C 6F 05 05 05
Decrypted plaintext: "Hello"
In the above example, the plaintext “Hello” is padded with three bytes (0x05) to match the block size of 8 bytes. During decryption, the same padding is expected, and if not found, an “Invalid Crypto Padding” error will be encountered.
Solution:
To resolve the “Invalid Crypto Padding” issue, ensure that the padding scheme used during encryption is the same as the one used during decryption. Make sure the padding is added correctly, and during decryption, the padding is verified and removed correctly.
If you are using a library or cryptographic framework, consult the documentation to understand the default padding scheme and ensure consistency throughout your encryption and decryption processes.