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I wonder why there is a limit of just 63 characters for the passphrase of WPA2-PSK. It's not even a power of two and looks very unusual to me, but surely there's some deeper meaning to this number.
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WPA2-PSK can be configured to use a password of up to 63 characters, which should be secure enough for any organization to adopt.
WPA2 AES encryption uses two keys : PTK nad GTK, each 128 bit long. AES is a block cipher, a type of symmetric key cipher that uses groups of bits of a fixed length - called blocks.
Key--The shared secret key for WPA Personal security. Enter a string of at least 8 characters to a maximum of 63 characters. Acceptable characters include upper and lower case alphabetic letters, the numeric digits, and special symbols such as @ and #.
According to the documentation of the standard, the length of an SSID should be a maximum of 32 characters (32 octets, normally ASCII letters and digits, though the standard itself doesn't exclude values). Some access point/router firmware versions use null-terminated strings and accept only 31 characters.
The PSK is derived from the passphrase using PBKDF2 key derivation function with SHA1 as the pseudo random function. The passphrase is an 8-63 character ASCII encoded string.
PSK = PBKDF2(PassPhrase, ssid, ssidLength, 4096, 256)
The PSK is 32 bytes (256 bits), often displayed as 64 hex characters.
According to the 802.11i specification:
A pass-phrase is a sequence of between 8 and 63 ASCII-encoded characters. The limit of 63 comes from the desire to distinguish between a pass-phrase and a PSK displayed as 64 hexadecimal characters.
So the difference is just to distinguish a 64 hex character PSK from a 8-63 character ASCII passhprase.
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