109 lines
4.3 KiB
Nim
109 lines
4.3 KiB
Nim
# beacon_chain
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# Copyright (c) 2022 Status Research & Development GmbH
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# Licensed and distributed under either of
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# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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import
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chronicles,
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bearssl/rand,
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nimcrypto/[hmac, utils],
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stew/[byteutils, results]
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from std/base64 import encode
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from std/json import JsonNode, `$`, `%*`
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from std/options import Option, get, isNone
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from std/os import `/`
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from std/strutils import replace
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export rand, results
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when (NimMajor, NimMinor) < (1, 4):
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{.push raises: [Defect].}
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else:
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{.push raises: [].}
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proc base64urlEncode(x: auto): string =
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# The only strings this gets are internally generated, and don't have
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# encoding quirks.
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base64.encode(x, safe = true).replace("=", "")
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func getIatToken*(time: int64): JsonNode =
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# https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.1/src/engine/authentication.md#jwt-claims
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# "Required: iat (issued-at) claim. The EL SHOULD only accept iat timestamps
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# which are within +-60 seconds from the current time."
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#
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# https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.6 describes iat
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# claims.
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#
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# https://pyjwt.readthedocs.io/en/stable/usage.html#issued-at-claim-iat shows
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# an example of an iat claim: {"iat": 1371720939}
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%* {"iat": time}
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proc getSignedToken*(key: openArray[byte], payload: string): string =
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# https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.1/src/engine/authentication.md#jwt-specifications
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# "The EL MUST support at least the following alg: HMAC + SHA256 (HS256)"
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# https://datatracker.ietf.org/doc/html/rfc7515#appendix-A.1.1
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const jwsProtectedHeader =
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base64urlEncode($ %* {"typ": "JWT", "alg": "HS256"}) & "."
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# In theory, std/json might change how it encodes, and it doesn't per-se
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# matter but can also simply specify the base64-encoded form directly if
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# useful, since it's never checked here on its own.
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static: doAssert jwsProtectedHeader == "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9."
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let signingInput = jwsProtectedHeader & base64urlEncode(payload)
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signingInput & "." & base64urlEncode(sha256.hmac(key, signingInput).data)
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proc getSignedIatToken*(key: openArray[byte], time: int64): string =
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getSignedToken(key, $getIatToken(time))
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proc checkJwtSecret*(
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rng: var HmacDrbgContext, dataDir: string, jwtSecret: Option[string]):
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Result[seq[byte], cstring] =
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# If such a parameter is given, but the file cannot be read, or does not
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# contain a hex-encoded key of 256 bits, the client should treat this as an
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# error: either abort the startup, or show error and continue without
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# exposing the authenticated port.
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const SECRET_LEN = 32
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if jwtSecret.isNone:
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# If such a parameter is not given, the client SHOULD generate such a
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# token, valid for the duration of the execution, and store it the
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# hex-encoded secret as a jwt.hex file on the filesystem. This file can
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# then be used to provision the counterpart client.
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#
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# https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.1/src/engine/authentication.md#key-distribution
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const jwtSecretFilename = "jwt.hex"
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let jwtSecretPath = dataDir / jwtSecretFilename
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let newSecret = rng.generateBytes(SECRET_LEN)
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try:
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writeFile(jwtSecretPath, newSecret.to0xHex())
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except IOError as exc:
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# Allow continuing to run, though this is effectively fatal for a merge
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# client using authentication. This keeps it lower-risk initially.
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warn "Could not write JWT secret to data directory",
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jwtSecretPath,
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err = exc.msg
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return ok(newSecret)
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try:
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# TODO replace with separate function
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let lines = readLines(jwtSecret.get, 1)
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if lines.len > 0:
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# Secret JWT key is parsed in constant time using nimcrypto:
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# https://github.com/cheatfate/nimcrypto/pull/44
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let secret = utils.fromHex(lines[0])
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if secret.len == SECRET_LEN:
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ok(secret)
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else:
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err("JWT secret not 256 bits")
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else:
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err("no hex string found")
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except IOError:
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err("couldn't open specified JWT secret file")
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except ValueError:
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err("invalid JWT hex string")
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