Reports the byte sizes that FIPS 203 fixes for one ML-KEM parameter set: the public (encapsulation) key, the secret (decapsulation) key, the ciphertext, the key-generation seed and the shared secret. Use it to check a key or ciphertext before storing or sending it, or to size a buffer or a database column, so a caller never has to hard-code the numbers.
Value
A named integer vector of five elements, all in bytes:
public (the encapsulation key), secret (the
decapsulation key), ciphertext, seed and shared
(the shared secret), named as kemkg() and
kemencap() name their
results.
Details
The values come from the native core and are those of FIPS 203, Table 3:
| 512 | 768 | 1024 | |
| encapsulation key | 800 | 1184 | 1568 |
| decapsulation key | 1632 | 2400 | 3168 |
| ciphertext | 768 | 1088 | 1568 |
| seed | 64 | 64 | 64 |
| shared secret | 32 | 32 | 32 |
Hex strings from kemkg() and
kemencap() are twice these
lengths in characters. Error: lvl other than one whole number
512, 768 or 1024.
Examples
kemsz(768)
#> public secret ciphertext seed shared
#> 1184 2400 1088 64 32
# the shared secret is 32 bytes at every level: the level buys
# security margin, not a longer secret
vapply(c(512, 768, 1024),
function(l) kemsz(l)[["shared"]], integer(1))
#> [1] 32 32 32
# check a ciphertext's length before sending it
key <- kemkg(768)
ct <- kemencap(key)$ciphertext
nchar(ct) / 2 == kemsz(768)[["ciphertext"]]
#> [1] TRUE
# an unknown level is an error, not a default
try(kemsz(2048))
#> Error : `lvl` must be one of 512, 768 or 1024