The algorithm mostly used in cryptography for secure data transmission is the AES (Advanced Encryption Standard). AES is a symmetric key algorithm that encrypts data in blocks, providing a secure means for protecting sensitive information. It is widely adopted in various applications, from securing financial transactions to safe communications over the internet. Its strength lies in its key lengths of 128, 192, or 256 bits, making it resistant to brute-force attacks. As a result, AES is considered a standard for data encryption and plays a crucial role in modern cryptographic applications.