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Byte lengths of an HQC parameter set

Source: R/hqc.R
hqcsz.Rd

Reports the byte lengths that the HQC specification fixes for a security level: the encapsulation (public) key, the decapsulation (secret) key, the ciphertext, the key-generation seed, the encapsulation randomness and the shared secret. Use it to validate stored keys and ciphertexts, or to size storage, without hard-coding numbers.

Usage

hqcsz(lvl, ver = c("v5", "round4"))

Arguments

lvl

Security level: 1, 3 or 5 (or 128, 192, 256 for the same three). There is no default.

ver

"v5" (the default) or "round4", as in hqckg().

Value

A named integer vector of byte lengths: public (the encapsulation key), secret (the decapsulation key), ciphertext, seed (key generation), message and salt (encapsulation randomness) and shared (the shared secret), named as hqckg() and hqcencap() name their results.

Details

The values come from the compiled implementation, so they are the sizes it actually uses. For version = "v5" (specification of 2025-08-22):

HQC-1HQC-3HQC-5
encapsulation key224145147237
decapsulation key232146027333
ciphertext4433897814421
seed323232
message162432
salt161616
shared secret323232

For version = "round4" the codes are the same but the key encoding differs: the seed is 96, 104 or 112 bytes and the shared secret 64 bytes. A level other than 1, 3, 5 (or 128, 192, 256) is an error.

See also

hqckg(), kemsz() for ML-KEM.

Examples

hqcsz(1)
#>     public     secret ciphertext       seed    message       salt     shared 
#>       2241       2321       4433         32         16         16         32 

# code-based keys and ciphertexts are larger than ML-KEM's at the same
# category; the shared secret is 32 bytes at every level (64 in round 4)
rbind(HQC = hqcsz(3)[c("public", "ciphertext")],
      MLKEM = kemsz(768)[c("public", "ciphertext")])
#>       public ciphertext
#> HQC     4514       8978
#> MLKEM   1184       1088
rbind(v5 = hqcsz(1), round4 = hqcsz(1, "round4"))
#>        public secret ciphertext seed message salt shared
#> v5       2241   2321       4433   32      16   16     32
#> round4   2249   2305       4433   96      16   16     64

# check a stored public key's length
key <- hqckg(1)
nchar(key$public) / 2 == hqcsz(1)[["public"]]
#> [1] TRUE

# an unknown level is refused rather than mapped to a default
try(hqcsz(2))
#> Error : `lvl` must be one of 1, 3 or 5 (HQC-1, HQC-3, HQC-5) or 128, 192, 256