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libp2p AutoTLS Client

Lifecycle Stage	Maturity	Status	Latest Revision
1A	Working Draft	Active	r1, 2025-05-21

Authors: @gmelodie

Interest Group: TBD

Overview
General Flow
Requesting challenge from ACME server
Sending challenge to AutoTLS broker
Signalling challenge completion to ACME server
Downloading certificate
Complete certificate issuance example
References

Overview

Most modern web browsers only establish TLS connections with peers that present certificates issued by a recognized Certificate Authority (CA). Self-signed certificates are generally not accepted. To obtain a CA-issued certificate, a requester must complete an ACME (Automatic Certificate Management Environment) challenge. This typically involves provisioning a DNS TXT record on a domain the requester controls.

However, most libp2p peers do not own or control domain names, making it impractical for them to complete DNS-based ACME challenges and, by extension, to obtain trusted TLS certificates. This limitation hinders direct communication between libp2p peers and standard web browsers.

AutoTLS addresses this problem by introducing an AutoTLS broker — a server that controls a domain and facilitates ACME challenges on behalf of libp2p peers. A peer can request the AutoTLS broker to fulfil an ACME DNS challenge on its behalf. Once the broker sets the appropriate DNS record, the requesting peer proceeds to notify the ACME server. The ACME server validates the challenge against the broker's domain, and if successful, issues a valid certificate.

This mechanism allows libp2p peers to obtain CA-issued certificates without needing to possess or manage their own domain names.

General Flow

The following is the general flow of a successful certificate request and subsequent issuance using AutoTLS. Here, "node" refers to the machine running a libp2p peer and requesting the challenge, while "broker" and "AutoTLS broker", which are used interchangeably, is the server that will fulfil the ACME challenge on behalf of the node.

Node requests a challenge from the ACME server.
Node sends the challenge to the broker.
Broker tests node and sets DNS record (fulfilling challenge).
Node queries DNS until it sees that the broker has fulfilled the challenge.
Node signals to ACME server that challenge is fulfilled.
ACME server checks challenge in broker.
Node sends CSR to finalize certificate request.
Node polls ACME server until certificate is ready for download.
Node downloads certificate.

Paramenters

Parameter	Description	Reasonable Default
`dns_poll_interval`	Time the node SHOULD wait between of DNS queries	1 second
`dns_timeout`	The maximum time a node SHOULD wait for DNS records to be set	3 minutes
`acme_poll_interval`	Time the node SHOULD wait between ACME GET requests	1 second
`acme_timeout`	The maximum time a node SHOULD wait for an ACME resource status to change	3 minutes

Requesting challenge from ACME server

The node starts a libp2p peer with public IPv4 and support for the identify protocol.
The node encodes its PeerID as multibase base36 of the CIDv1 of the multihash with the libp2p-key (0x72) multicodec:
1. Transform PeerID into a multihash mh.
2. Encode mh using CIDv1 with the libp2p-key multicodec(0x72).
3. Encode the CID data using multibase base36, which is the same as regular base36 without trimming leading zeroes and including a leading k or K) to get b36peerid.
Note: "CID data" are the raw bytes that compose the CID, not richer CID objects that contain more information.
The node generates a key mykey as specified in RFC7518.
The node registers an account on the ACME server (e.g. production or staging servers for Let's Encrypt).
1. Send a GET request to the /directory endpoint of the ACME server, and extract the newAccount value from the JSON response, which will be the registration URL we'll use.
2. Send JWT-signed POST request to registration URL with the following payload: {"termsOfServiceAgreed": true} (a contact field containing a list of mailto:bob@example.org contact information strings can also be optionally specified in the payload). The POST body is signed using JWT with mykey and nonce (nonce is a number returned by sending a GET request to the ACME server at the URL specified in directory["newNonce"]). The JSON payload using an RSA-256 key before JWT-signing should look like:
```
{
  "header": {
    "alg": "RS256",
    "typ": "JWT",
    "nonce": "`nonce`",
    "url": "`url`",
    "jwk": {
      "kty": "RSA",
      "n": "`mykey.n`",
      "e": "`mykey.e`"
    }
  },
  "claims": {
    "payload": {
      "termsOfServiceAgreed": true,
      "contact": [
        "mailto:alice@example.com",
        "mailto:bob@example.com"
      ]
    }
  }
}
```
The final body of any ACME request should look like: json { "payload": "`claims.toBase64`", "protected": "`header.toBase64`", "signature": "`base64UrlEncode(signature)`" }
The node MUST save the kid present in the location header of the ACME server's response for in future requests to ACME server.
The node requests a certificate for the *.{b36peerid}.libp2p.direct domain from the ACME server by issuing a POST request using the same JWT signature scheme (and a new nonce) but using the kid field instead of the jwk field and containing the following JSON payload:
```
{
  "identifiers": [
    {
      "type": "dns",
      "value": "*.{b36peerid}.libp2p.direct"
    }
  ]
}
```
From the ACME server response, the node MUST save the entry with type of dns-01 and derive keyAuthorization from that.
From the ACME server response's dns-01 field, the node MUST also save the value on the url field of the JSON body, here called chalUrl. This is used in the ACME signalling phase.
From the ACME server response's, the node MUST also save the value on the location header, here called orderUrl. This is used in the ACME signalling phase.
From the ACME server response's, the node MUST also save the value on the finalize field of the JSON body, here called finalizeUrl. This is used in the ACME signalling phase.

Sending challenge to AutoTLS broker

The node sends keyAuthorization to the AutoTLS broker (e.g. registration.libp2p.direct). This requires a peer ID authentication between node and broker:
1. Node sends GET request to the AutoTLS broker's /v1/_acme-challenge endpoint and extracts challenge-node, public-key and opaque from the www-authenticate response header.
2. Node generates 32-character-long random string to be sent as a challengeServer.
Note: At the time of writing the PeerID Authentication specification does not contain recommendations about challenge length, but the official go-libp2p implementation uses 32 characters. 3. Node generates sig, headers and payload as follows, where peer-privkey is the private key of the node's libp2p peer and multiaddrs is a list of string representations of the libp2p peer's multiaddresses:
```
	sig = base64URL(
		peer-privkey.sign(
			bytes(varint + "challenge-node={challenge-node}") +
			bytes(varint + "hostname={hostname}") +
			bytes(varint + "server-public-key={public-key}")
		)
	)

	headers = {
		"Content-Type": "application/json",
		"User-Agent": "some-user-agent",
		"authorization": "libp2p-PeerID public-key=\"{nodePublicKeyB64}\", opaque=\"{opaque}\", challenge-server=\"{challengeServer}\", sig=\"{sig}\""
	}

    payload = {
        "value": keyAuthorization,
        "addresses": multiaddrs
    }
```
Note: varint is a protobuf varint field that encodes the length of each of the key=value string.

Note: The node SHOULD only include multiaddresses that contain public IPv4 addresses in multiaddrs. 4. Node sends a POST request to /v1/_acme-challenge endpoint using payload as HTTP body and headers as HTTP headers. 5. Node SHOULD save the bearer token from the authentication-info response header, and use it for following requests to the AutoTLS broker.

Signalling challenge completion to ACME server

Node SHOULD query DNS records (TXT _acme-challenge.{b36peerid}.libp2p.direct and A dashed-public-ip-address.{b36peerid}.libp2p.direct) until they are set by the AutoTLS broker.

Note: Here, dashed-public-ip-address is the public IPv4 address of the node in which the node received the confirmation dial from the broker. For example, if the node has two public IPv4 addresses 1.1.1.1 and 8.8.8.8, and the broker dialed it through 1.1.1.1, then the node SHOULD query the A 1-1-1-1.{b36peerid}.libp2p.direct.

Note: The node SHOULD NOT poll DNS for longer than dns_timeout. After dns_timeout, the communication is considered failed. What to do after dns_timeout has passed is left as an implementation decision.

Node notifies the ACME server about challenge completion so that the ACME server can lookup the DNS resource records that the AutoTLS broker has set. The notification is done in the form of a POST request to chalUrl with an empty HTTP body ({}).
1. Node sends an empty signed JSON payload ({}) to the ACME server using the kid obtained from the initial ACME registration and gets the response from the server (completedResponse).
2. Node extracts url field from completedResponse's JSON body. The extracted URL is named checkUrl in this document.
The node polls the ACME server by sending a GET HTTP request to checkUrl with an empty body, and sign using the kid of the registered account. The node MUST poll the ACME server until it receives a response with status: valid or status: invalid field, meaning that the challenge checking was successful or not, respectively.

Note: The node SHOULD NOT send more than one request every acme_interval to the ACME server. The node SHOULD use exponential backoff to increase time between retries. After acme_timeout, the communication has failed. What to do after acme_timeout has passed is left as an implementation decision.

Downloading certificate

Node finalizes the certificate request:
1. Generate CSR for the *.{b36peerid}.libp2p.direct domain.
2. Encode the CSR with URL safe base 64 (b64CSR).
3. Send a kid signed POST request to finalizeUrl with JSON HTTP body of {"csr": b64CSR}.
Node MUST poll ACME server by sending GET requests to orderUrl until the ACME server's response contains a status field with a value different than processing.

Node downloads finalized certificate by sending a GET request to certDownloadUrl. certDownloadUrl is found in the certificate field of the JSON HTTP body of a response to a GET request to orderUrl.

Complete certificate issuance example

In this example the node at 142.93.194.175 and with peer ID 12D3KooWATZi2wFwQxQ14Z3q24TDNWKap6f8W5ryLE6Da4RMfsxy.

Node encodes its peer ID to multicode base 36: k51qzi5uqu5dgf513xbrfjl4smgo2eh1x8p8y6grzsf1oz0reiy56p65tds3s6

Node generates an RSA key and registers with ACME server by issuing a POST HTTP request to https://acme-staging-v02.api.letsencrypt.org with the following JSON body:

{
  "header": {
    "alg": "RS256",
    "typ": "JWT",
    "nonce": "1jOOXM0FEc7tL_RH3PbFWf5Ml4QXTrtG-d2faH_j68L9K27-768",
    "url": "https://acme-staging-v02.api.letsencrypt.org/acme/new-acct",
    "jwk": {
      "kty": "RSA",
      "n": "xImaldcbdCDn_IHSa2qeYjOhQ5PLuqIWLXEwQvvzD6eUIC8MteHvSM9Yj4tUGUzQ6Vic7j5j3npZhrmXMv3FiwIpQgsqDEiXSyriST7zYSPtQUcZr17gEqk9Rxjewl77HKkTej34IQ7JLaHzx5owJVtNsfBI36NPQiBCDaEBMht0E5zyMa83fTlNqnVnyMAqOR7CxctsxmYkoyyYeA_hV0gJfOBzUHls_ENHP67dQ2eVYGJ0gU7ldaK7lsWw10ieNCEDjbDT9E50HAdQt4UO1c_6rD8jzD0UjS2xtO6wrJpkmUnkt71WoQXWIWjoTvhl15dqLwyx_jeW-C6ISpwh1eWdrcM0z0TZpOZQEODg1IJppOEQZsBYeSZg4El5rt1IKcllp6euWlHPopreFNcEUrYZ76uQQLuRyQ2AM_caUITFi6e0ZgTea2COuy4vof2ZJTBZP8uE4aHUdXOMYrDO6TVnXYA7mYJ6jkyp-X9OjzGSst6yRY5Qm-uCmBEuVtoN",
      "e": "AQAB"
    }
  },
  "claims": {
    "termsOfServiceAgreed": true
  }
}

Which, after JWT signing, becomes:

{
  "payload": "eyJpZGVudGlmaWVycyI6W3sidHlwZSI6ImRucyIsInZhbHVlIjoiKi5rNTFxemk1dXF1NWRnZjUxM3hicmZqbDRzbWdvMmVoMXg4cDh5NmdyenNmMW96MHJlaXk1NnA2NXRkczNzNi5saWJwMnAuZGlyZWN0In1dfQ",
  "protected": "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsIm5vbmNlIjoiWW8xc2xCY2RhV3FZREoyanFPYkhIb0dUZkZkQlJubzJzM2pzRGxQN2VNdXo5T1lDNWpBIiwidXJsIjoiaHR0cHM6Ly9hY21lLXN0YWdpbmctdjAyLmFwaS5sZXRzZW5jcnlwdC5vcmcvYWNtZS9uZXctb3JkZXIiLCJraWQiOiJodHRwczovL2FjbWUtc3RhZ2luZy12MDIuYXBpLmxldHNlbmNyeXB0Lm9yZy9hY21lL2FjY3QvMjAxNDI3MzQ0In0",
  "signature": "f2oPdLiFYwvv7_KLaiSlBgJJh3brXDA9_wPfw52UB_GTU0eL_9y9-oX8WJJcEU87juUWUuML3eEOT4zjUY1EK2ri-rR_8AO2QngpxpWbo86wUM-XwiXk35uGelpW0QvCQw_x16AWK6xr0Rm1gSbnVkxOMrMBl-2xQYyXILwLmEuTq76C2vt2ZzrLhcV-6BKUla2lkgaZKPK3dpTYL0_i0pEybb28Ree5SERHpxihxFTO1ggvLJosbdlGOtAvCc7x-aZhTcuwhjlCRNLi0rnsFRNh3PJc-_Kz5B2Uv_OoTktWg_0vrUU_OFBuf4lHl5lb82cl5NxRH9ieX673rsh9in9l9Nr-Gt3g8SdiY29LTMwOy37MmhhNcL7MjUcseI05FOhLFxyc3dUxsG92VSDwJ_1JQIQH7EGJ6vP_dDPustMlvzNX_qHV2TjN6XpAv2tECmK5enU7qfnhTXbPihvz7MY1_PAlxJSWmBq-ui_sovN85YNJWBZ-tIPOPtqPMZDT"
}

Node requests a certificate for *.k51qzi5uqu5dgf513xbrfjl4smgo2eh1x8p8y6grzsf1oz0reiy56p65tds3s6.libp2p.direct by issuing a POST request to https://acme-staging-v02.api.letsencrypt.org/acme/new-order with the following JSON body:

{
  "header": {
    "alg": "RS256",
    "typ": "JWT",
    "nonce": "Yo1slBcdaWqYDJ2jqObHHoGTfFdBRno2s3jsDlP7eMuz9OYC5jA",
    "url": "https://acme-staging-v02.api.letsencrypt.org/acme/new-order",
    "kid": "https://acme-staging-v02.api.letsencrypt.org/acme/acct/201427344"
  },
  "claims": {
    "identifiers": [
      {
        "type": "dns",
        "value": "*.k51qzi5uqu5dgf513xbrfjl4smgo2eh1x8p8y6grzsf1oz0reiy56p65tds3s6.libp2p.direct"
      }
    ]
  }
}

From the ACME server's response, node saves orderUrl, chalUrl and finalizeUrl:

orderUrl: https://acme-staging-v02.api.letsencrypt.org/acme/order/201427344/24815752984
chalUrl: https://acme-staging-v02.api.letsencrypt.org/acme/chall/201427344/17523856954/k8-vYA
finalizeUrl: https://acme-staging-v02.api.letsencrypt.org/acme/finalize/201427344/24815752984

Node generates keyAuthorization (jP5hwrZwCbP_qeeET_qAa9pgG0YulNaR0ivruESzCrE) from the following dns-01 object:

{
  "type": "dns-01",
  "url": "https://acme-staging-v02.api.letsencrypt.org/acme/chall/201427344/17523856954/k8-vYA",
  "status": "pending",
  "token": "nE2YGvFXzAy6UsFjYxqYOyA6rxZ7VJeQppsQ72hHyPM"
}

Node authenticates with AutoTLS broker at "https://registration.libp2p.direct/v1/_acme-challenge" (refer to the peer ID authentication spec for guidance and examples) and sends the following JSON body:
```
{
  "value": "jP5hwrZwCbP_qeeET_qAa9pgG0YulNaR0ivruESzCrE",
  "addresses": [
    "/ip4/142.93.194.175/tcp/49309"
  ]
}
```

Note: the node's multiaddresses are /ip4/127.0.0.1/tcp/49309, /ip4/142.93.194.175/tcp/49309, /ip4/10.17.0.5/tcp/49309, and /ip4/10.108.0.2/tcp/49309, but only /ip4/142.93.194.175/tcp/49309 contains a public IPv4 address, so node SHOULD only send that.

Node saves the bearer token (bJNzn30OvOSIPsd0UtMygo4ccjUMXkwHONRHc46oyTx7ImlzLXRva2VuIjp0cnVlLCJwZWVyLWlkIjoiMTJEM0tvb1dBVFppMndGd1F4UTE0WjNxMjRURE5XS2FwNmY4VzVyeUxFNkRhNFJNZnN4eSIsImhvc3RuYW1lIjoicmVnaXN0cmF0aW9uLmxpYnAycC5kaXJlY3QiLCJjcmVhdGVkLXRpbWUiOiIyMDI1LTA1LTIyVDE0OjAxOjU4LjY1NzAyMDQ4OFoifQ==) from the broker's authentication-info response header:

Authentication-Info: libp2p-PeerID sig="hysWRh0SAQX6MkhNIwf0rgyjqbV9wkjMDhNobVhHybBE3CygrOAfEPTkvgrrePX5XTGt1FO-4--VBbJas8BtCQ==", bearer="bJNzn30OvOSIPsd0UtMygo4ccjUMXkwHONRHc46oyTx7ImlzLXRva2VuIjp0cnVlLCJwZWVyLWlkIjoiMTJEM0tvb1dBVFppMndGd1F4UTE0WjNxMjRURE5XS2FwNmY4VzVyeUxFNkRhNFJNZnN4eSIsImhvc3RuYW1lIjoicmVnaXN0cmF0aW9uLmxpYnAycC5kaXJlY3QiLCJjcmVhdGVkLXRpbWUiOiIyMDI1LTA1LTIyVDE0OjAxOjU4LjY1NzAyMDQ4OFoifQ=="

Node queries DNS records: TXT _acme-challenge.k51qzi5uqu5dgf513xbrfjl4smgo2eh1x8p8y6grzsf1oz0reiy56p65tds3s6.libp2p.direct and A 142-93-194-175.k51qzi5uqu5dgf513xbrfjl4smgo2eh1x8p8y6grzsf1oz0reiy56p65tds3s6.libp2p.direct until it receives a non-empty response from DNS servers.

Node notifies ACME server about challenge completion by issuing an empty POST request to chalUrl with kid JWT signing:

{
  "header": {
    "alg": "RS256",
    "typ": "JWT",
    "nonce": "Yo1slBcd5jWarMN9llbXOVII-htMZpSZBumnZAaKdyzqjyNfREg",
    "url": "https://acme-staging-v02.api.letsencrypt.org/acme/chall/201427344/17523856954/k8-vYA",
    "kid": "https://acme-staging-v02.api.letsencrypt.org/acme/acct/201427344"
  },
  "claims": {}
}

Node extracts checkUrl (https://acme-staging-v02.api.letsencrypt.org/acme/chall/201427344/17523856954/k8-vYA) from url field from ACME server's response body:

{
  "type": "dns-01",
  "url": "https://acme-staging-v02.api.letsencrypt.org/acme/chall/201427344/17523856954/k8-vYA",
  "status": "pending",
  "token": "nE2YGvFXzAy6UsFjYxqYOyA6rxZ7VJeQppsQ72hHyPM"
}

Node polls the ACME server by sending GET HTTP requests to checkUrl until it receives a response with status: valid:

{
  "type": "dns-01",
  "url": "https://acme-staging-v02.api.letsencrypt.org/acme/chall/201427344/17523856954/k8-vYA",
  "status": "valid",
  "validated": "2025-05-22T14:01:59Z",
  "token": "nE2YGvFXzAy6UsFjYxqYOyA6rxZ7VJeQppsQ72hHyPM",
  "validationRecord": [
    {
      "hostname": "k51qzi5uqu5dgf513xbrfjl4smgo2eh1x8p8y6grzsf1oz0reiy56p65tds3s6.libp2p.direct"
    }
  ]
}

Node creates the CSR:

MIIBJzCBzgIBADAAMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE-xJPmWkXNCxikFNfjX-YpNpVUlwVE75FqiLzQKqz0oSRGChnxEiCPXSYW6XYfy7RyYtoaMKJB8oYjpuoZau2U6BsMGoGCSqGSIb3DQEJDjFdMFswWQYDVR0RBFIwUIJOKi5rNTFxemk1dXF1NWRnZjUxM3hicmZqbDRzbWdvMmVoMXg4cDh5NmdyenNmMW96MHJlaXk1NnA2NXRkczNzNi5saWJwMnAuZGlyZWN0MAoGCCqGSM49BAMCA0gAMEUCIA_wWAa07lkYDlXVs8QBxX9XI7ATyMT8KIWirx2dBwyVAiEA9anNGq3BssBdMKW-QHKdOPqcv7lzaB64vTjpfciyfr4="

And sends it to finalizeUrl:

{
  "header": {
    "alg": "RS256",
    "typ": "JWT",
    "nonce": "Yo1slBcdhW7xgUkJ0DzYeH1otfpMMbjbXD3xlf7TM1lneccMLHI",
    "url": "https://acme-staging-v02.api.letsencrypt.org/acme/finalize/201427344/24815752984",
    "kid": "https://acme-staging-v02.api.letsencrypt.org/acme/acct/201427344"
  },
  "claims": {
    "csr": "MIIBJzCBzgIBADAAMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE-xJPmWkXNCxikFNfjX-YpNpVUlwVE75FqiLzQKqz0oSRGChnxEiCPXSYW6XYfy7RyYtoaMKJB8oYjpuoZau2U6BsMGoGCSqGSIb3DQEJDjFdMFswWQYDVR0RBFIwUIJOKi5rNTFxemk1dXF1NWRnZjUxM3hicmZqbDRzbWdvMmVoMXg4cDh5NmdyenNmMW96MHJlaXk1NnA2NXRkczNzNi5saWJwMnAuZGlyZWN0MAoGCCqGSM49BAMCA0gAMEUCIA_wWAa07lkYDlXVs8QBxX9XI7ATyMT8KIWirx2dBwyVAiEA9anNGq3BssBdMKW-QHKdOPqcv7lzaB64vTjpfciyfr4="
  }
}

Node polls orderUrl until the ACME server's response contains a status field with value different than processing:

{
  "status": "valid",
  "expires": "2025-05-29T14:01:58Z",
  "identifiers": [
    {
      "type": "dns",
      "value": "*.k51qzi5uqu5dgf513xbrfjl4smgo2eh1x8p8y6grzsf1oz0reiy56p65tds3s6.libp2p.direct"
    }
  ],
  "authorizations": [
    "https://acme-staging-v02.api.letsencrypt.org/acme/authz/201427344/17523856954"
  ],
  "finalize": "https://acme-staging-v02.api.letsencrypt.org/acme/finalize/201427344/24815752984",
  "certificate": "https://acme-staging-v02.api.letsencrypt.org/acme/cert/2cd1c21b2b77127e4d394eb16eb073f9248d"
}

Node downloads the certificate by sending a GET request to certDownloadUrl (https://acme-staging-v02.api.letsencrypt.org/acme/cert/2cd1c21b2b77127e4d394eb16eb073f9248d), which is the certificate field of the finalize request's response:

References

Announcing AutoTLS: Bridging the Gap Between libp2p and the Web

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