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docs: Improve documentation

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PapaTutuWawa 2022-08-03 16:50:27 +02:00
parent 45d0c57305
commit f897431692
1 changed files with 62 additions and 54 deletions
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116
lib/src/double_ratchet.dart
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@ -72,7 +72,9 @@ class OmemoDoubleRatchet {
final Map<SkippedKey, List<int>> mkSkipped = {};
/// This is performed by the initiating entity
/// Create an OMEMO session using the Signed Pre Key [spk], the shared secret [sk] that
/// was obtained using a X3DH and the associated data [ad] that was also obtained through
/// a X3DH.
static Future<OmemoDoubleRatchet> initiateNewSession(OmemoPublicKey spk, List<int> sk, List<int> ad) async {
final dhs = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
final dhr = spk;
@ -92,11 +94,12 @@ class OmemoDoubleRatchet {
);
}
/// This is performed by the accepting entity
/// Create an OMEMO session that was not initiated by the caller using the used Signed
/// Pre Key keypair [spk], the shared secret [sk] that was obtained through a X3DH and
/// the associated data [ad] that was also obtained through a X3DH.
static Future<OmemoDoubleRatchet> acceptNewSession(OmemoKeyPair spk, List<int> sk, List<int> ad) async {
final dhs = spk;
return OmemoDoubleRatchet(
dhs,
spk,
null,
sk,
null,
@ -108,6 +111,53 @@ class OmemoDoubleRatchet {
);
}
Future<List<int>?> _trySkippedMessageKeys(OMEMOMessage header, List<int> ciphertext) async {
final key = SkippedKey(
OmemoPublicKey.fromBytes(header.dhPub, KeyPairType.x25519),
header.n,
);
if (mkSkipped.containsKey(key)) {
final mk = mkSkipped[key]!;
mkSkipped.remove(key);
return decrypt(mk, ciphertext, concat([sessionAd, header.writeToBuffer()]), sessionAd);
}
return null;
}
Future<void> _skipMessageKeys(int until) async {
if (nr + maxSkip < until) {
throw SkippingTooManyMessagesException();
}
if (ckr != null) {
while (nr < until) {
final newCkr = await kdfCk(ckr!, kdfCkNextChainKey);
final mk = await kdfCk(ckr!, kdfCkNextMessageKey);
ckr = newCkr;
mkSkipped[SkippedKey(dhr!, nr)] = mk;
nr++;
}
}
}
Future<void> _dhRatchet(OMEMOMessage header) async {
pn = header.n;
ns = 0;
nr = 0;
dhr = OmemoPublicKey.fromBytes(header.dhPub, KeyPairType.x25519);
final newRk = await kdfRk(rk, await dh(dhs, dhr!, 0));
rk = newRk;
ckr = newRk;
dhs = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
final newNewRk = await kdfRk(rk, await dh(dhs, dhr!, 0));
rk = newNewRk;
cks = newNewRk;
}
/// Encrypt [plaintext] using the Double Ratchet.
Future<RatchetStep> ratchetEncrypt(List<int> plaintext) async {
final newCks = await kdfCk(cks!, kdfCkNextChainKey);
final mk = await kdfCk(cks!, kdfCkNextMessageKey);
@ -126,65 +176,23 @@ class OmemoDoubleRatchet {
);
}
Future<List<int>?> trySkippedMessageKeys(OMEMOMessage header, List<int> ciphertext) async {
final key = SkippedKey(
OmemoPublicKey.fromBytes(header.dhPub, KeyPairType.x25519),
header.n,
);
if (mkSkipped.containsKey(key)) {
final mk = mkSkipped[key]!;
mkSkipped.remove(key);
return decrypt(mk, ciphertext, concat([sessionAd, header.writeToBuffer()]), sessionAd);
}
return null;
}
Future<void> skipMessageKeys(int until) async {
if (nr + maxSkip < until) {
throw SkippingTooManyMessagesException();
}
if (ckr != null) {
while (nr < until) {
final newCkr = await kdfCk(ckr!, kdfCkNextChainKey);
final mk = await kdfCk(ckr!, kdfCkNextMessageKey);
ckr = newCkr;
mkSkipped[SkippedKey(dhr!, nr)] = mk;
nr++;
}
}
}
Future<void> dhRatchet(OMEMOMessage header) async {
pn = header.n;
ns = 0;
nr = 0;
dhr = OmemoPublicKey.fromBytes(header.dhPub, KeyPairType.x25519);
final newRk = await kdfRk(rk, await dh(dhs, dhr!, 0));
rk = newRk;
ckr = newRk;
dhs = await OmemoKeyPair.generateNewPair(KeyPairType.x25519);
final newNewRk = await kdfRk(rk, await dh(dhs, dhr!, 0));
rk = newNewRk;
cks = newNewRk;
}
/// Decrypt a [ciphertext] that was sent with the header [header] using the Double
/// Ratchet. Returns the decrypted (raw) plaintext.
///
/// Throws an SkippingTooManyMessagesException if too many messages were to be skipped.
Future<List<int>> ratchetDecrypt(OMEMOMessage header, List<int> ciphertext) async {
// Check if we skipped too many messages
final plaintext = await trySkippedMessageKeys(header, ciphertext);
final plaintext = await _trySkippedMessageKeys(header, ciphertext);
if (plaintext != null) {
return plaintext;
}
if (header.dhPub != await dhr?.getBytes()) {
await skipMessageKeys(header.pn);
await dhRatchet(header);
await _skipMessageKeys(header.pn);
await _dhRatchet(header);
}
await skipMessageKeys(header.n);
await _skipMessageKeys(header.n);
final newCkr = await kdfCk(ckr!, kdfCkNextChainKey);
final mk = await kdfCk(ckr!, kdfCkNextMessageKey);
ckr = newCkr;