codec_multikey/
encode.rs

1// SPDX-FileCopyrightText: Copyright © 2026 ReallyMe LLC. All rights reserved
2//
3// SPDX-License-Identifier: Apache-2.0
4
5use codec_multibase::bytes_to_multibase58btc;
6use codec_multicodec::{KeyMaterialKind, MULTICODEC_TABLE, VARIABLE_KEY_LENGTH};
7
8use crate::error::{classify_multikey_codec, CodecNameReason, MultikeyError};
9
10/// Maximum accepted RSA public-key DER payload in a multikey.
11///
12/// The supported RSA multicodec is variable-length because DER size depends on
13/// modulus size and encoding details. A 4 KiB cap leaves room for common public
14/// keys while preventing unbounded base58 and FFI amplification through RSA.
15pub const MAX_RSA_PUBLIC_KEY_DER_LEN: usize = 4 * 1024;
16
17/// Encodes a public key as a multibase (base58btc) multikey string.
18///
19/// Fails closed: returns an error if the codec name is unknown or the key
20/// length does not match the codec.
21pub fn encode_multikey(codec_name: &str, public_key: &[u8]) -> Result<String, MultikeyError> {
22    let (canonical_codec_name, spec) = MULTICODEC_TABLE
23        .iter()
24        .find(|(name, _)| *name == codec_name)
25        .ok_or(MultikeyError::UnknownCodecName {
26            reason: CodecNameReason::Unsupported,
27        })?;
28
29    if spec.key_material != KeyMaterialKind::PublicKey {
30        return Err(MultikeyError::UnknownCodecName {
31            reason: CodecNameReason::Unsupported,
32        });
33    }
34
35    if spec.key_length == VARIABLE_KEY_LENGTH && public_key.is_empty() {
36        return Err(MultikeyError::KeyLengthMismatch {
37            codec: classify_multikey_codec(canonical_codec_name),
38            expected: spec.key_length,
39            actual: public_key.len(),
40        });
41    }
42
43    if *canonical_codec_name == "rsa-pub" && public_key.len() > MAX_RSA_PUBLIC_KEY_DER_LEN {
44        return Err(MultikeyError::KeyTooLarge {
45            codec: classify_multikey_codec(canonical_codec_name),
46            max: MAX_RSA_PUBLIC_KEY_DER_LEN,
47            actual: public_key.len(),
48        });
49    }
50
51    if spec.key_length != VARIABLE_KEY_LENGTH && public_key.len() != spec.key_length {
52        return Err(MultikeyError::KeyLengthMismatch {
53            codec: classify_multikey_codec(canonical_codec_name),
54            expected: spec.key_length,
55            actual: public_key.len(),
56        });
57    }
58
59    let capacity =
60        spec.codec
61            .len()
62            .checked_add(public_key.len())
63            .ok_or(MultikeyError::KeyLengthMismatch {
64                codec: classify_multikey_codec(canonical_codec_name),
65                expected: spec.key_length,
66                actual: public_key.len(),
67            })?;
68    let mut payload = Vec::with_capacity(capacity);
69    payload.extend_from_slice(spec.codec);
70    payload.extend_from_slice(public_key);
71
72    bytes_to_multibase58btc(&payload).map_err(|_| MultikeyError::EncodedPayloadTooLarge)
73}
codec_multikey/encode.rs

codec_multikey/
encode.rs
