This document describes a new addressing scheme for Monero.
Chapters 1-2 are intended for general audience.
Chapters 3-7 contain technical specifications.
- 1. Introduction
- 2. Features
- 3. Notation
- 4. Wallets
- 5. Addresses
- 6. Address encoding
- 7. Test vectors
- References
Sometime in 2023, Monero plans to adopt a new transaction protocol called Seraphis [1], which enables much larger ring sizes than the current RingCT protocol. However, due to a different key image construction, Seraphis is not compatible with CryptoNote addresses. This means that each user will need to generate a new set of addresses from their existing private keys. This provides a unique opportunity to vastly improve the addressing scheme used by Monero.
The CryptoNote-based addressing scheme [2] currently used by Monero has several issues:
- Addresses are not suitable as human-readable identifiers because they are long and case-sensitive.
- View-only wallets need key images to be imported to detect spent outputs [3].
- Too much information about the wallet is leaked when scanning is delegated to a third party.
- Generating subaddresses requires view access to the wallet. This is why many merchants prefer integrated addresses [4].
- Addresses are susceptible to man-in-the-middle (MITM) attacks [5].
- Subaddresses that belong to the same wallet can be linked via the Janus attack [6].
Jamtis is a new addressing scheme that was developed specifically for Seraphis and tackles all of the shortcomings of CryptoNote addresses that were mentioned above. Additionally, Jamtis incorporates two other changes related to addresses to take advantage of this large upgrade opportunity:
- A new 16-word mnemonic scheme called Polyseed [7] that will replace the legacy 25-word seed for new wallets.
- The removal of integrated addresses and payment IDs [8].
Jamtis addresses, when encoded as a string, start with the prefix xmr1
and typically consist of 181 characters. Example of an address: xmr1majob1977bw3ympyh2yxd7hjymrw8crc9kinodkm8d3wdu8jdhf3fkdpmgxfkbywbb9mdwkhkya4jtfnod5h7s49bfyji1936w19tyf396ypjo9n64runqjrxwp6k2s3phxwm6wrb5cob6c1ntrg2mugeocwdgnnr7u7bgknya9arksrj
There is no longer any "main address" - all Jamtis addresses are equivalent to a subaddress.
Jamtis introduces a short recipient identifier (RID) that can be calculated for every wallet and every address. RID consists of 25 alphanumeric characters that are separated by hyphens for better readability. The RID for the above address is regne-hwbna-u21gh-b54no-8x36q
. Instead of comparing long addresses, users can compare the much shorter RID. RIDs are also suitable to be communicated via phone calls, text messages or handwriting to confirm a recipient's address. This allows the address itself to be transferred via an insecure channel.
To protect from MITM attacks, Jamtis addresses can be optionally signed by the owner of the wallet. The main use cases are:
When Alice and Bob meet, Bob can write his RID on a piece of paper and give it to Alice. When Bob sends Alice an address in the future, Alice will know the address belongs to Bob because it is signed with a key that matches the RID Bob gave her.
When proving a payment [9], Alice can convince Charlie that the address she made a payment to belongs to Bob, because the address was signed by Bob's key. If the address were not signed, Bob could claim that the address is not his, but Alice's own address.
Dave runs an online shop at https://eshop.example.com. To assure his customers, he can create a special DNS record under the domain name eshop.example.com that validates his Monero public key and he can provide certified Monero addresses to all his customers. When shopping at Dave's website, Alice can feel safe to send her Monero to the provided address, because her wallet software will confirm that the address is owned by the domain eshop.example.com.
Jamtis introduces new wallet tiers below view-only wallet. One of the new wallet tiers called "FindReceived" is intended for wallet-scanning and only has the ability to calculate view tags [10]. It cannot generate wallet addresses or decode output amounts.
View tags can be used to eliminate 99.6% of outputs that don't belong to the wallet. If provided with a list of wallet addresses, this tier can also link outputs to those addresses. Possible use cases are:
A wallet can have a "FindReceived" component that stays connected to the network at all times and filters out outputs in the blockchain. The full wallet can thus be synchronized at least 256x faster when it comes online (it only needs to check outputs with a matching view tag).
If the "FindReceived" private key is provided to a 3rd party, it can preprocess the blockchain and provide a list of potential outputs. This reduces the amount of data that a light wallet has to download by a factor of at least 256. The third party will not learn which outputs actually belong to the wallet and will not see output amounts.
Jamtis introduces new wallet tiers that are useful for merchants.
This tier is intended for merchant point-of-sale terminals. It can generate (and certify) addresses on demand, but otherwise has no access to the wallet (i.e. it cannot recognize any payments in the blockchain).
This wallet tier combines the Address generator tier with the ability to also view received payments (including amounts). It is intended for validating paid orders. It cannot see outgoing payments and received change.
Jamtis supports full view-only wallets that can identify spent outputs (unlike legacy view-only wallets), so they can display the correct wallet balance and list all incoming and outgoing transactions.
Janus attack is a targeted attack that aims to determine if two addresses A, B belong to the same wallet. Janus outputs are crafted in such a way that they appear to the recipient as being received to the wallet address B, while secretly using a key from address A. If the recipient confirms the receipt of the payment, the sender learns that they own both addresses A and B.
Jamtis prevents this attack by allowing the recipient to recognize a Janus output.
The detection of outputs received to current Monero subaddresses is based on a lookup table. This can sometimes cause the wallet to miss outputs that are received to subaddresses not present in the lookup table [16].
Jamtis addresses and outputs contain an encrypted address tag which enables a more robust output detection mechanism that does not rely on a lookup table and can reliably detect outputs sent to arbitrary wallet addresses.
- Fixed-size integers are serialized in little endian byte order.
- Private keys are serialized as 256-bit integers.
- String constants are serialized in ASCII encoding and always include an implicit null byte at the end.
- Elliptic curve points are serialized as 256-bit integers, with the lower 255 bits being the y-coordinate of the point and the most significant bit being the parity of the x-coordinate.
- The function
BytesToInt256(x)
deserializes a 256-bit little-endian integer from a 32-byte input. - The operator
||
concatenates the serialized representations of its inputs. - The function
Padb(x)
outputsx || 0x00 || 0x00 || ... || 0x00
where the number of padding zero bytes is such that the total length of the output is a multiple ofb
bytes.
The function H(x)
refers to the keccak-256 hash function. The following other functions based on H
are used:
H1(x) = H(x)[0]
is hash function with an output length of 1 byte.H8(x) = H(x)[0:8]
is hash function with an output length of 8 bytes.H16(x) = H(x)[0:16]
is hash function with an output length of 16 bytes.Hs(x) = BytesToInt256(H(x)) mod ℓ
refers to a "hash to scalar" function, whereℓ
is a prime number.Hp(x)
refers to an unspecified "hash to point" function, which outputs elliptic curve points.KeyDerive(k, x) = Hs(Pad136(k) || x)
is a function to derive elliptic curve private keys.SecretDerive(k, x) = H(Pad136(k) || x)
is a function to derive secret keys for symmetric cryptography.
This specification assumes the use of the ed25519 elliptic curve, which includes a cyclic subgroup 𝔾
of prime order ℓ = 2252 + 27742317777372353535851937790883648493
.
- Uppercase letters usually refer to elements of
𝔾
. - Lowercase letters usually refer to elements of
Zℓ
(scalars). - Scalar multiplication is denoted by a space between the scalar and the group element, e.g.
K = k G
. - Scalar multiplication may be prepended with the number
8
, which means that the point is also multiplied by the ed25519 cofactor to ensure the result belongs to the group𝔾
.
The following three base points are used:
Point | Derivation | Serialized (hex) |
---|---|---|
G |
generator of 𝔾 |
5866666666666666666666666666666666666666666666666666666666666666 |
U |
Hp("seraphis U") |
126582dfc357b10ecb0ce0f12c26359f53c64d4900b7696c2c4b3f7dcab7f730 |
X |
Hp("seraphis X") |
4017a126181c34b0774d590523a08346be4f42348eddd50eb7a441b571b2b613 |
The function BlockEnc(k, x)
refers to the application of the Blowfish [11] permutation using the secret key k
on the 64-bit little-endian integer x
. The function BlockDec(k, x)
refers to the application of the inverse permutation using the key k
.
In order to save space, certified addrfesses use a recoverable Schnorr signature scheme specified in this section as a set of two functions SignIdent
and RecoverIdent
.
This function accepts two parameters: a private key k
and an abitrary octet string data
.
- Select a deterministic nonce
r = KeyDerive(k, data || "SignIdent nonce")
- Calculate
R = r G
- Calculate
e = Hs(R || data)
- Calculate
s = (e-1*k - r) mod ℓ
- Return the tuple
(R,s)
This function accepts two parameters: the signature tuple (R,s)
and an abitrary octet string data
.
- Calculate
e = Hs(R || data)
- Calculate
u = e*s mod ℓ
- Calculate
K = u G + e R
- Return
K
If an adversary changes R
or data
, the resulting public key K
will change unpredictably.
If an adversary replaces s
with s' = (s + e-1*m) mod ℓ
, the public key will change to K' = K + m G
. For this reason, the private signing key k
must never be constructed by adding an offset to an existing key.
We define a HashIdent
function that accepts an arbitrary octet string data
and returns H16(data)
encoded in base32 using the ID32 scheme [12].
Each wallet consists of two main private keys and a timestamp:
Field | Type | Description |
---|---|---|
km |
private key | wallet master key |
kvb |
private key | view-balance key |
birthday |
timestamp | date when the wallet was created |
The master key km
is required to spend money in the wallet and the view-balance key kvb
provides full view-only access.
The birthday
timestamp is important when restoring a wallet and determines the blockchain height where scanning for owned outputs should begin.
Standard Jamtis wallets are generated as a 16-word Polyseed mnemonic [7], which contains a secret seed value used to derive the wallet master key and also encodes the date when the wallet was created. The key kvb
is derived from the master key.
Field | Derivation |
---|---|
km |
BytesToInt256(polyseed_key) mod ℓ |
kvb |
kvb = KeyDerive(km, "view-balance key") |
birthday |
from Polyseed |
Multisignature wallets are generated in a setup ceremony, where all the signers collectively generate the wallet master key km
and the view-balance key kvb
.
Field | Derivation |
---|---|
km |
setup ceremony |
kvb |
setup ceremony |
birthday |
setup ceremony |
Legacy pre-Seraphis wallets define two private keys:
- private spend key
ks
- private view-key
kv
Legacy standard wallets can be migrated to the new scheme based on the following table:
Field | Derivation |
---|---|
km |
km = ks |
kvb |
kvb = KeyDerive(km, "view-balance key") |
birthday |
entered manually |
Legacy wallets cannot be migrated to Polyseed and will keep using the legacy 25-word seed.
Legacy multisignature wallets can be migrated to the new scheme based on the following table:
Field | Derivation |
---|---|
km |
km = ks |
kvb |
kvb = kv |
birthday |
entered manually |
There are additional keys derived from kvb
:
Key | Name | Derivation | Used to |
---|---|---|---|
kga |
generate-address key | kga = SecretDerive(kvb, "generate-address key") |
generate addresses |
kfr |
find-received key | kfr = KeyDerive(kvb, "find-received key") |
scan for received outputs |
kid |
identify-wallet key | kid = KeyDerive(kga, "identify-wallet key") |
certify addresses |
ket |
encrypt-tag key | ket = SecretDerive(kga, "encrypt-tag key") |
encrypt address tags |
The keys kga
and kfr
separate the view access into two tiers. The first one provides the ability to derive all public addresses that belong to the wallet and the latter is used to calculate the sender-receiver shared secret when scanning for received outputs.
The key kga
has two additional child keys kid
and ket
, which are used in different cryptographic algorithms when generating an address.
The following figure shows the overall hierarchy of wallet keys. Note that the relationship between km
and kvb
only applies to standard (non-multisignature) wallets.
Tier | Knowledge | Off-chain capabilities | On-chain capabilities |
---|---|---|---|
AddrGen | kga |
generate public addresses | none |
FindReceived | kfr |
recognize all public wallet addresses | eliminate 99.6% of non-owned outputs (up to § 5.3.5), link output to an address (except of change and self-spends) |
ViewReceived | kga, kfr |
all | view all received except of change and self-spends (up to § 5.3.14) |
ViewAll | kvb |
all | view all |
Master | km |
all | all |
This wallet tier can generate public addresses for the wallet. It doesn't provide any blockchain access.
Thanks to view tags, this tier can eliminate 99.6% of outputs that don't belong to the wallet. If provided with a list of wallet addresses, it can also link outputs to those addresses (but it cannot generate addresses on its own). This tier should provide a noticeable UX improvement with a limited impact on privacy. Possible use cases are:
- An always-online wallet component that filters out outputs in the blockchain. A higher-tier wallet can thus be synchronized 256x faster when it comes online.
- Third party scanning services. The service can preprocess the blockchain and provide a list of potential outputs with pre-calculated spend keys (up to § 5.2.4). This reduces the amount of data that a light wallet has to download by a factor of at least 256.
This level combines the tiers AddrGen and FindReceived and provides the wallet with the ability to see all incoming payments to the wallet, but cannot see any outgoing payments and change outputs. It can be used for payment processing or auditing purposes.
This is a full view-only wallet than can see all incoming and outgoing payments (and thus can calculate the correct wallet balance).
This tier has full control of the wallet.
There are 3 global wallet public keys. These keys are not usually published.
Key | Name | Value |
---|---|---|
Ks |
wallet spend key | Ks = kvb X + km U |
Kid |
identify-wallet key | Kid = kid G |
Kfr |
find-received key | Kfr = kfr G |
The keys Ks
and Kfr
are required by lower wallet tiers.
For better UX when opening or restoring a wallet, the wallet is identified by HashIdent("Monero RID" || Kid)
.
Jamtis wallets can generate up to 256 different addresses. An address is identified by a 64-bit integer j
with the most significant 8 bits set to zero.
Each Jamtis address consists of three public keys and an encrypted tag:
K1j = Ks + kxj X
K2j = kaj Kfr
K3j = kaj G
tj = BlockEnc(ket, j)
The private keys kaj
and kxj
are derived as follows:
Keys | Name | Derivation |
---|---|---|
kaj |
address keys | kaj = KeyDerive(kga, "address key" || j) |
kxj |
spend key extensions | kxj = KeyDerive(kga, "key extension" || j) |
All addresses contain 3 unique public keys and are thus unlinkable by default.
Wallet software MUST NOT generate addresses with j >= 256
.
When sending amount a
to someone else's address (K1, K2, K3, t)
, the sender does the following:
- Generate a random nonzero scalar
r
fromZℓ
. - Calculate the ephemeral public key
Ke = r K3
- Calculate the derived key
Kd = 8*r K2
- Calculate the view tag
v = H1("view tag", Kd)
- Calculate the shared secret
q = Hs("sender-receiver secret", Kd)
- Encrypt the address tag
t~ = t XOR H8("address tag", q)
- Derive a one-time output public key
Ko = K1 + q X
- Calculate the blinding factor
b = Hs("blind", q, r G)
- Encrypt the amount
a~ = a XOR H8("amount", q, r G)
- Calculate the amount commitment
C = b G + a H
- Output
(Ke, v, t~, Ko, a~, C)
The receiver does the following to examine a potential output (Ke, v, t~, Ko, a~, C)
:
- Calculate the nominal derived key
Kd' = 8*kfr Ke
- Calculate the nominal view tag
v' = H1("view tag", Kd')
- If
v' != v
, abort. - Calculate the nominal shared secret
q' = Hs("sender-receiver secret", Kd')
- Decrypt the nominal address tag
t' = t~ XOR H8("address tag", q)
- Decrypt the nominal address index
j' = BlockDec(ket, t')
- If
j' >= 256
, abort. - Derive the address spend key
K1j = Ks + kxj X
- If
K1j != Ko - q' X
, abort. - Derive
r' G = Ke / kaj
- Decrypt the nominal amount
a'= a~ XOR H8("amount", q, r' G)
- Calculate the nominal blinding factor
b' = Hs("blind", q, r' G)
- Calculate the nominal amount commitment
C' = b' G + a' H
- If
C' != C
, abort (possible Janus attack). - Calculate the partial private spend key
ksp = kvb + kxj + q
- Derive the linking tag
Kt = (Ks - kvb X) / ksp
- Set the boolean
s
to the spend status of the linking tagKt
- Output the private values
(a, b, j, ksp, s)
Change outputs and self-spends are special because the sender is the same as the receiver. There are heuristics that can be applied by lower wallet tiers to recognize when outputs are being spent based on the presence of outputs that send funds back to the wallet [13].
To protect from such attacks, the output construction and recognition is modified for change and self-spends.
When a wallet software is constructing a transaction to an address (K1, K2, K3, t)
, the following IsSelfSpend
function MUST be called to detect self-spends:
- Decrypt the nominal address index
j' = BlockDec(ket, t)
- If
j' >= 256
, returnfalse
. - Derive the address spend key
K1j = Ks + kxj X
- Return
K1j == K1
.
- The shared secret from § 5.2.4 is calculated as
q = DeriveKey(kvb, "self secret" || Ke)
- For change outputs, the encrypted address tag from § 5.2.6 is set to
t~ = j XOR H8("address tag", q)
- For self-spends, the encrypted address tag from § 5.2.6 is set to
t~ = (j + 256) XOR H8("address tag", q)
- The blinding factor from § 5.2.8 is calculated as
b = Hs("blind", q)
- The encrypted amount from § 5.2.9 is calculated as
a~ = a XOR H8("amount", q)
The distinction between change outputs and self-spends is done to preserve the transaction history (self-spends should be visible in the history, change outputs not).
Change outputs and self-spends can only be detected by wallet tiers ViewAll and Master because it requires the private key kvb
. Whenever an output with a matching view tag is discovered in a transaction that spends a previous wallet output:
- Derive the nominal shared secret as
q' = DeriveKey(kvb, "self secret" || Ke)
- Decrypt the nominal address index
j' = t~ XOR H8("address tag", q')
- If
j' >= 257
, abort. - If
j >= 256
, this may be a self-spend. Setj = j - 256
. Otherwise this may be a change output. - Derive the address spend key
K1j = Ks + kxj X
- If
K1j != Ko - q' X
, abort. - Decrypt the nominal amount
a'= a~ XOR H8("amount", q)
- Calculate the nominal blinding factor
b' = Hs("blind", q)
- Continue from § 5.3.13
Jamtis has a small impact on transaction size.
The size of 2-output transactions is increased by 8 bytes. The encrypted payment ID is removed, but the transaction needs two encrypted address tags t~
(one for the recipient and one for the change). Both outputs can use the same value of Ke
.
Since there are no "main" addresses anymore, the TX_EXTRA_TAG_PUBKEY
field can be removed from transactions with 3 or more outputs.
Instead, all transactions with 3 or more outputs will require one 40-byte tuple (Ke, t~)
per output.
An address has the following overall structure:
Field | Size (bytes) | Description |
---|---|---|
Header | 6* | human-readable address header (§ 6.2) |
K1 |
32 | address key 1 |
K2 |
32 | address key 2 |
K3 |
32 | address key 3 |
t |
8 | address tag |
Signature | 64 | for certified addresses (§ 6.3) |
Checksum | 8* | (§ 6.4) |
* The header and the checksum are already encoded in base32
The address starts with a human-readable header, which has the following format consisting of 6 alphanumeric characters:
"xmr" <version char> <network type char> <address type char>
Unlike the rest of the address, the header is never encoded and is the same for both the binary and textual representations. The string is not null terminated.
The software decoding an address shall abort if the first 3 bytes are not 0x78 0x6d 0x72
("xmr").
The "xmr" prefix serves as a disambiguation from legacy addresses that start with "4" or "8". Additionally, base58 strings that start with the character x
are invalid due to overflow [14], so legacy Monero software can never accidentally decode a Jamtis address.
The version character is "1"
. The software decoding an address shall abort if a different character is encountered.
network char | network type |
---|---|
"t" |
testnet |
"s" |
stagenet |
"m" |
mainnet |
The software decoding an address shall abort if an invalid network character is encountered.
type char | address type |
---|---|
"a" |
anonymous |
"c" |
certified |
The software decoding an address shall abort if an invalid address type character is encountered.
All Jamtis addresses are by default unlinkable to the wallet that created them. However, the owner of the wallet may optionally attach a signature that links the address to the wallet identity key Kid
. The signature is present if the address type character in the address header is "c"
.
The signature field is encoded as:
(R,s) = SignIdent(kid, "Monero address signature" || Header || K1 || K2 || K3 || t)
When parsing a certified address, the wallet software can calculate the receiver's identity key as:
Kid = RecoverIdent((R,s), "Monero address signature" || Header || K1 || K2 || K3 || t)
The purpose of the checksum is to detect accidental corruption of the address. The checksum consists of 8 characters and is calculated using a BCH code [15] with a degree-8 polynomial. The checksum can detect all errors affecting 4 or fewer characters and will fail to detect more errors with a chance of less than 1 in 1012. [TODO: Specify the BCH polynomial.]
An address can be encoded into a string as follows:
address_string = header + base32(data) + checksum
where header
is the 6-character human-readable header string (already in base32), data
refers to the 3 address public keys, the address tag and the optional signature. The checksum
is the 8-character checksum (already in base32). The base32 encoding uses the character set ybndrfg8ejkmcpqxot1uwis2a345h769
.
Address type | length |
---|---|
anonymous | 181 |
certified | 283 |
While the canonical form of an address is lower case, when encoding an address into a QR code, the address should be converted to upper case to take advantage of the more efficient alphanumeric encoding mode.
Because addresses are bulky and opaque, Jamtis defines a concise, more human-friendly identifier for each address, called the Recipient identifier (RID). RIDs are calculated depednding on the address type:
Address type | RID |
---|---|
anonymous | HashIdent("Monero RID" || Header || K1 || K2 || K3 || t) |
certified | HashIdent("Monero RID" || Kid) |
There are 4 ways how an RID may be validated when sending to an address:
- It may be already present in the sender's address book.
- It may be entered manually by the user. In this case, it's best to obtain the RID from the receiver using a different communication channel than the one used to transfer the address.
- The user may enter a domain name (e.g.
example.com
) and the RID is validated by performing a TXT DNS lookup of a subdomain equal to the RID (e.g.regne-hwbna-u21gh-b54no-8x36q.example.com
). [TODO: Specify the contents of the TXT field.] - The user may enter an onion address and the public key is decoded from the onion address (v3 onion addresses encode an ed25519 public key that's also usable in Monero) and compared to the address public key.
When sending to an address, wallet software should follow this authentication workflow:
- The address is parsed and verified that it's well-formed.
- The RID is calculated.
- If the RID is present in the local address book, the recipient's name is loaded and displayed with a green check mark. Skip to step 8.
- The user is presented with a "recipient validation dialog", where they are asked to enter an RID or a domain name.
- If the address RID matches the one that was entered or obtained via DNS or the onion domain, the RID is displayed as validated with a yellow check mark. Skip to step 7.
- If the RID doesn't match the address, no DNS record was found or the user dismisses the dialog, the RID is displayed with a red cross mark as "unverified".
- The user is asked to enter the remaining payment parameters.
TODO
- https://github.com/UkoeHB/Seraphis
- https://bytecoin.org/old/whitepaper.pdf
- https://www.getmonero.org/resources/user-guides/view_only.html
- monero-project/meta#299 (comment)
- https://www.reddit.com/r/Monero/comments/mcvuxc/beware_crypto_stealing_malware/
- https://web.getmonero.org/2019/10/18/subaddress-janus.html
- https://github.com/tevador/polyseed
- monero-project/monero#7889
- https://www.getmonero.org/resources/user-guides/prove-payment.html
- monero-project/research-lab#73
- https://en.wikipedia.org/wiki/Blowfish_(cipher)
- https://github.com/tevador/id32
- https://gist.github.com/tevador/50160d160d24cfc6c52ae02eb3d17024#gistcomment-4006358
- https://github.com/monero-project/monero/blob/319b831e65437f1c8e5ff4b4cb9be03f091f6fc6/src/common/base58.cpp#L157
- https://en.wikipedia.org/wiki/BCH_code
- monero-project/monero#8138