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
hqc_sizes(level, version = c("v5", "round4"))Arguments
- level
Security level: 1, 3 or 5 (or 128, 192, 256 for the same three). There is no default.
- version
"v5"(the default) or"round4", as inhqc_keygen().
Value
A named integer vector: encapsulation_key, decapsulation_key,
ciphertext, seed (key generation), message and salt
(encapsulation randomness) and shared_secret, all in bytes.
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-1 | HQC-3 | HQC-5 | |
| encapsulation key | 2241 | 4514 | 7237 |
| decapsulation key | 2321 | 4602 | 7333 |
| ciphertext | 4433 | 8978 | 14421 |
| seed | 32 | 32 | 32 |
| message | 16 | 24 | 32 |
| salt | 16 | 16 | 16 |
| shared secret | 32 | 32 | 32 |
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
hqc_keygen(),
kem_sizes() for ML-KEM.
Examples
hqc_sizes(1)
#> encapsulation_key decapsulation_key ciphertext seed
#> 2241 2321 4433 32
#> message salt shared_secret
#> 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 = hqc_sizes(3)[c("encapsulation_key", "ciphertext")],
ML_KEM = kem_sizes(768)[c("encapsulation_key", "ciphertext")])
#> encapsulation_key ciphertext
#> HQC 4514 8978
#> ML_KEM 1184 1088
rbind(v5 = hqc_sizes(1), round4 = hqc_sizes(1, "round4"))
#> encapsulation_key decapsulation_key ciphertext seed message salt
#> v5 2241 2321 4433 32 16 16
#> round4 2249 2305 4433 96 16 16
#> shared_secret
#> v5 32
#> round4 64
# check a stored public key's length
key <- hqc_keygen(1)
nchar(key$public) / 2 == hqc_sizes(1)[["encapsulation_key"]]
#> [1] TRUE
# an unknown level is refused rather than mapped to a default
try(hqc_sizes(2))
#> Error : `level` must be one of 1, 3 or 5 (HQC-1, HQC-3, HQC-5)