What is Key size?
{{distinguish|Key space}} In [[cryptography]], '''key size''' or '''key length''' is the size (measured in bits or bytes) of the [[key (cryptography)|key]] used in a cryptographic algorithm (such as a [[cipher]]). Typical key sizes in modern symmetric ciphers are 128, 192, and 256 bits. Older symmetric ciphers used only 40, 56, or 64 bits, which can be broken by [[Brute force attack|brute force]]. 128 bits is considered secure against brute-force by traditional computers, but not [[quantum computer]]s. 192 and 256 bit keys are considered quantum-safe, and [[Advanced Encryption Standard|AES]] keys of these lengths are approved for protecting [[Classified information|top secret]] information. [[Public-key cryptography|Asymmetric (public key)]] ciphers such as [[RSA algorithm|RSA]] need a much longer key to be secure. RSA keys are typically at least 2048 bits. A large key size alone does not necessarily mean a cipher is secure - there are many insecure ciphers which have a large key size but have other design flaws that allow them to be broken. {{Cryptography public-key}} {{math-stub}} [[Category:Cryptography]]