cubesigner-go-sdk

README

CubeSigner Go SDK

CubeSigner is a hardware-backed, non-custodial platform for securely managing cryptographic keys. This repository is the Go SDK for programmatically interacting with CubeSigner services.

CubeSigner background

The Cubist team built CubeSigner to address the key security vs key availability tradeoff: right now, many teams are forced to keep keys available in memory and therefore exposed to attackers, or try to keep keys safe—usually only at rest—at serious latency and engineering cost. CubeSigner addresses this problem by giving developers low-latency access to hardware-backed key generation and signing. During each of these operations, CubeSigner safeguards their users' keys in HSM-sealed Nitro Enclaves—combining cold wallet security with hot wallet speed and simplicity.

Right now, the CubeSigner SDK supports signing for EVM chains like Ethereum and Avalanche, and non-EVM chains Bitcoin and Solana. Support for more chains is in the works!

Installing the SDK

Add the CubeSigner Go SDK to your project with:

go get github.com/cubist-labs/cubesigner-go-sdk

Logging into CubeSigner

Before running the "getting started" examples below (or tests later), you must log into your CubeSigner organization using the cs command-line tool, e.g.,

cs login owner@example.com --env '<gamma|prod|...>'

Getting Started

In this section we are going to walk through a simple CubeSigner setup. We'll create a signing key, then sign some EVM transactions, and then add a security policy to restrict the kinds of transactions that CubeSigner is allowed to sign.

To start, we'll instantiate the top-level ApiClient object from an existing CubeSigner management session already stored on disk (remember, you must already be logged in).

Let's also assume that the following imports are available to all the examples below.

import (
    "fmt"
    "log"
    "os"
    "strings"
    "time"

    "github.com/pquerna/otp/totp"
    "github.com/cubist-labs/cubesigner-go-sdk/session"
    "github.com/cubist-labs/cubesigner-go-sdk/client"
    "github.com/cubist-labs/cubesigner-go-sdk/models"
    "github.com/cubist-labs/cubesigner-go-sdk/spec/env"
    "github.com/cubist-labs/cubesigner-go-sdk/utils/ref"
)

We also use the following utilities to help us handle errors:

func assert(cond bool, v ...any) {
	if !cond {
		log.Panic(v...)
	}
}

func assertError(err error, errorMsg string) {
	assert(err != nil, "Error expected, got nil")
	assert(
		strings.Contains(err.Error(), errorMsg),
		"Expected the error message to contain ", errorMsg, " but it doesn't: ", err.Error())
}

func assertNil(err error) {
	assert(err == nil, "Expected nil, got: ", err)
}

Instantiate the Session Manager

Next, we need to instantiate the SessionManager, which manages the session auth and refresh tokens behind the scenes.

We can do this by, for example, loading a session token from the default location on disk (which is where the cs login command saves it):

manager, err := session.NewJsonSessionManager(nil)
assertNil(err)

Use the Client

Finally, we can create the API client to make a request:

apiClient, err := client.NewApiClient(manager)
assertNil(err)

Get User and Org info

We can now obtain some information about the logged-in user and the organization the user belongs to:

// Get user info
userInfo, err := apiClient.AboutMe()
assertNil(err)

// each user has a globally unique ID
userId := userInfo.UserId
fmt.Println(userId)

// Ids of all organizations this user is a member of
allOrgs := userInfo.Orgs
fmt.Println(allOrgs)

// Get org information
orgInfo, err := apiClient.GetOrg()
assert(err == nil && orgInfo.Enabled)

There is a lot more to do with an organization, like creating/listing keys, creating/listing roles, setting up org-wide security policies, etc.

For the rest of this tutorial, we assume the logged-in user is a member of at least one organization.

Create a Key

Next, let's create a key that we'll later use to sign an Ethereum transaction. For that, we need a key of type SecpEthAddr.

createKeyRequest := models.CreateKeyRequest{KeyType: models.SecpEthAddr, Count: 1}
keysInfo, err := apiClient.CreateKey(createKeyRequest)
assertNil(err)

// read response to get the key info
secpKey := keysInfo.Keys[0]

Sign an Ethereum transaction

Lets create a dummy Eth1SignRequest.

TxBody := models.TypedTransaction{}
TxBody.FromTypedTransactionEip1559(models.TypedTransactionEip1559{
    To: ref.Of("0xff50ed3d0ec03ac01d4c79aad74928bff48a7b2b"),
    Type: "0x02",
    Gas: ref.Of("0x61a80"),
    MaxFeePerGas: ref.Of("0x2540be400"),
    MaxPriorityFeePerGas: ref.Of("0x3b9aca00"),
    Nonce: ref.Of("0"),
    Value: ref.Of("0x100"),
})

eth1Request := models.Eth1SignRequest{
    ChainId: int64(1),
    Tx: TxBody,
}

It seems we have everything in place to sign this request with the previously created key. However, attempting to do so fails with 403 Forbidden saying something like Session does not have the required scopes...

_, err = apiClient.EvmSign(secpKey.MaterialId, eth1Request)
// should fail with "Session does not have required scopes"
assertError(err, "Session does not have required scopes")

By default, the sessions created by the CLI cannot perform signing operations. All sessions have a series of scopes which determine what that session can be used for. We'll talk more about this later, but for now just know that we need a new session with the proper scopes:

sessionResp, err := apiClient.CreateSession("Go sdk readme signing demo", []models.Scope{"manage:key:get", "sign:*"}, nil)
assertNil(err)

signingClient, err := client.NewApiClient(session.NewMemorySessionManager(sessionResp.ResponseData))
assertNil(err)

// retry signing
eth1Resp, err := signingClient.EvmSign(secpKey.MaterialId, eth1Request)
assertNil(err)

fmt.Println(eth1Resp.ResponseData)

Access control with Role

CubeSigner uses roles to control access to keys when more than one user wants to use them. You can think of roles as groups that give certain users access to certain keys. To get started, let's create a Role and then simply call CreateSession on it:

roleResp, err := apiClient.CreateRole(&models.CreateRoleRequest{Name: "ReadmeGoTestRole"})
assertNil(err)

// Add key to the role
addKeyResp, err := apiClient.AddKeysToRole(roleResp.RoleId, models.AddKeysToRoleRequest{KeyIds: []string{secpKey.KeyId}})
assert(err == nil && addKeyResp.ResponseData != nil)

// Create a role session.
// Members of the role can create sessions which can only access keys in the role
roleSessionResp, err := apiClient.CreateRoleSession(roleResp.RoleId, models.CreateTokenRequest{
    Purpose: "Role session for Go SDK readme",
    // Role sessions implicitly have the "sign:*" scope
})
assertNil(err)

roleClient, err := client.NewApiClient(session.NewMemorySessionManager(roleSessionResp))
assertNil(err)

fmt.Printf("Created client for role %s\n", roleResp.RoleId)

Set security policies

When we add a Secp256k1 EVM key (i.e., key with type models.SecpEthAddr) to a role (as we did above), a client associated with that role allows us to sign any EVM transaction with that key. If that seems too permissive, we can attach a security policy to restrict the allowed usages of this key in this role.

For example, to restrict signing to transactions with a pre-approved recipient, we can attach a TxReceiver policy to our key:

updateKeyRequest := models.UpdateKeyRequest{
    Policy: ref.Of([]interface{}{map[string]string{
        "TxReceiver": "0xff50ed3d0ec03ac01d4c79aad74928bff48a7b2b",
    }}),
}
updateKeyInfoResp, err := apiClient.UpdateKey(secpKey.KeyId, updateKeyRequest)
assertNil(err)

secpKey = *updateKeyInfoResp.ResponseData

// sign evm transaction with role session
eth1Resp, err = roleClient.EvmSign(secpKey.MaterialId, eth1Request)
assert(err == nil && eth1Resp.ResponseData.RlpSignedTx != "")

Try changing the transaction receiver and verify that the transaction indeed gets rejected:

fmt.Println("Signing a transaction to a different receiver must be rejected")

TxBody = models.TypedTransaction{}
TxBody.FromTypedTransactionEip1559(models.TypedTransactionEip1559{
    To: ref.Of("0x0000000000000000000000000000000000000000"),
    Type: "0x02",
    Gas: ref.Of("0x61a80"),
    MaxFeePerGas: ref.Of("0x2540be400"),
    MaxPriorityFeePerGas: ref.Of("0x3b9aca00"),
    Nonce: ref.Of("0"),
    Value: ref.Of("0x100"),
})

newEth1Request := models.Eth1SignRequest{
    ChainId: int64(1),
    Tx: TxBody,
}

_, err = roleClient.EvmSign(secpKey.MaterialId, newEth1Request)
assertError(err, "Transaction receiver not allowed by policy")

Warning Setting new policies overwrites the previous ones.

Sign a raw blob

The ApiClient class exposes the BlobSign method, which signs an arbitrary (raw, uninterpreted) bag of bytes with a given key. This operation, however, is not permitted by default; it is permanently disabled for BLS keys, and for other key types it can be enabled by attaching an "AllowRawBlobSigning" policy:

// Create a Ed25519 key (e.g, for Cardano) and add it to our roleClient's role
createKeyRequest = models.CreateKeyRequest{KeyType: models.Ed25519CardanoAddrVk, Count: 1}
createKeyResp, err := apiClient.CreateKey(createKeyRequest)
assertNil(err)

// add to role
edKey := createKeyResp.Keys[0]
addKeysResp, err := apiClient.AddKeysToRole(roleResp.RoleId, models.AddKeysToRoleRequest{KeyIds: []string{edKey.KeyId}})
assert(err == nil && !addKeysResp.RequiresMfa())

// Sign raw blobs with our new ed key and the secp key we created before
for _, thisKey := range []models.KeyInfo{secpKey, edKey} {
    fmt.Printf("Confirming that raw blob with %s is rejected\n", thisKey.KeyType)
    blobSignRequest := models.BlobSignRequest {
        MessageBase64: "L1kE9g59xD3fzYQQSR7340BwU9fGrP6EMfIFcyX/YBc=",
    }

    _, err = roleClient.BlobSign(thisKey.KeyId, blobSignRequest)
    assertError(err, "Raw blob signing not allowed")

    // add Raw blob signing policy
    newPolicy := append(thisKey.Policy, "AllowRawBlobSigning")
    updateKeyRequest := models.UpdateKeyRequest{
        Policy: &newPolicy,
    }
    _, err := apiClient.UpdateKey(thisKey.KeyId, updateKeyRequest)
    assertNil(err)

    // try signing again
    sigResp, err := roleClient.BlobSign(thisKey.KeyId, blobSignRequest)
    assert(err == nil && sigResp.ResponseData.Signature != "")
}

Warning When signing a raw blob with a Secp256k1 key, the blob MUST be the output of a secure hash function like SHA-256, and must be exactly 32 bytes long. This is a strict requirement of the ECDSA signature algorithm used by Bitcoin, Ethereum, and other blockchains. Signing any byte string that is not the output of a secure hash function can lead to catastrophic security failure, including completely leaking your secret key.

Trying to sign an invalid message with a secp key will fail with 400 Bad Request saying Signature scheme: InvalidMessage.

Session Management

In the above examples we've used 3 different sessions:

1. A management session that we created using the CLI
2. A signing session that we created using (1)
3. A role session that we created used (1)

All ApiClients require a valid session in order to operate. In this section we'll dive into the specifics of sessions in the Go SDK.

Loading from disk

If you already have an active session in cs (the CubeSigner CLI), you can load it into the Go SDK with a simple helper (as we did earlier).

jsonManager, err := session.NewJsonSessionManager(nil)
assertNil(err)

Or we can use the CLI to create our own session explicitly for our Go client:

cs session create --role-id $ROLE_ID --scope sign-all --output json > session.json

Then we can load it by replacing nil with ref.Of("./session.json") like so:

jsonManager, err := session.NewJsonSessionManager(ref.Of("./session.json"))
assertNil(err)

// create a client to use this session manager
jsonSessionClient, err := client.NewApiClient(jsonManager)
assertNil(err)

fmt.Printf("Created client with session: %s\n", jsonSessionClient.Manager.Metadata())

Loading from Memory

If you already have the session information (SessionData in Go) in memory, you can load that directly into a client. We did so when creating a role session.

roleSessionResp, err = apiClient.CreateRoleSession(roleResp.RoleId, models.CreateTokenRequest{
    Purpose: "Role session for Go SDK readme",
})
assertNil(err)

// create a in-memory session manager
memManager := session.NewMemorySessionManager(roleSessionResp)

// create a client to use this session manager
memSessionClient, err := client.NewApiClient(memManager)
assertNil(err)

fmt.Printf("Created client with session: %s\n", memSessionClient.Manager.Metadata())

Loading from AWS Secrets Manager

Sessions stored in AWS Secrets Manager can be loaded with the AwsSessionManager. The AwsSessionManager does not auto-refresh the secret session and a separate rotation lambda is expected for this purpose.

secretId := "AwsCSSession"
// if AwsSecretSessionManagerOpts are nil, the default aws configuration is loaded
awsSessionManager, err := session.NewAwsSessionManager(secretId, nil)
assertNil(err)

[!WARNING]
Clients created this way will automatically refresh the session. If you try to use this session with another client, they will both try to refresh, leading to failures.

Clients, Managers, and Refreshing

As we've seen in the examples above, all client.ApiClients are constructed using the client.NewApiClient constructor. The client.NewApiClient constructor accepts a client.SessionManager. So far we have seen three different session managers:

• AwsSessionManager
• JsonSessionManager
• MemorySessionManager

These managers are responsible for keeping your session tokens refreshed and (optionally) persisted. Whenever your session tokens are refreshed, JsonSessionManager will write the new tokens to disk.

More complex managers can be written by implementing the client.SessionManager interface.

Create a session for an OIDC user

CubeSigner supports the OIDC standard for authenticating third-party users. This is typically done on the client-side rather than server-side.

First, we need an OIDC token. We can get one from Google or any other supported OIDC issuer. For the purpose of this example, we'll assume the OIDC token is stored in the OIDC_TOKEN environment variable.

oidcToken := os.Getenv("OIDC_TOKEN")
assert(oidcToken != "")

Before we can use the OIDC token for authentication, we must add an org policy to allow the particular issuer/audience pair from the token.

getOrgResp, err := apiClient.GetOrg()
assertNil(err)

if getOrgResp.Policy != nil {
    oldPolicy := getOrgResp.Policy
    fmt.Println(oldPolicy)
}

// parse OIDC token to get issuer and audience 
oidcSplits := strings.Split(oidcToken, ".")
decoded, err := base64.RawURLEncoding.DecodeString(oidcSplits[1])
assertNil(err)

var oidcPayload map[string]interface{}
err = json.Unmarshal(decoded, &oidcPayload)
assertNil(err)

// map issuer to audience for policy body
issMap := map[string][]string{oidcPayload["iss"].(string): {oidcPayload["aud"].(string)}}

// OidcAuthSources policy body
oidcAuthSourcesPolicy := map[string]interface{}{
    "OidcAuthSources": issMap,
}

// update org policy
updateOrgRequest := models.UpdateOrgRequest{
    Policy: ref.Of([]map[string]interface{}{oidcAuthSourcesPolicy}),
}
_, err = apiClient.UpdateOrg(updateOrgRequest)
assertNil(err)

Finally, exchange the OIDC token for a session.

env := env.Gamma
orgId := "Org#..."
oidcLoginRequest := models.OidcLoginRequest {
    Scopes: []models.Scope{"manage:mfa:*", "sign:*"},
}
oidcSessionResp, err := client.OidcAuth(env, orgId, oidcToken, oidcLoginRequest)
assertNil(err)

oidcClient, err := client.NewApiClient(session.NewMemorySessionManager(oidcSessionResp.ResponseData))
assertNil(err)

Set up TOTP for a user

To manage a user we need a session bound to that user. It doesn't matter if that user is native to CubeSigner or a third-party OIDC user. For that purpose, in this section we are going to use the previously created oidcClient instance.

To set up TOTP, we first call the UserResetTotpInit method to initiate a TOTP reset procedure on the client-side.

fmt.Printf("Setting up TOTP for user %s\n", *userInfo.Email)
totpResetResp, err := oidcClient.UserResetTotpInit(nil)
assertNil(err)

If the user has already configured TOTP (or any other form of MFA), this response will require multi factor authentication. In that case, for example, call totpApprove and provide the code for the existing TOTP to proceed:

totpSecret := os.Getenv("CS_USER_TOTP_SECRET")

if totpResetResp.RequiresMfa() {
    fmt.Println("Resetting TOTP requires MFA")
    totpCode, err := totp.GenerateCode(totpSecret, time.Now())
    assertNil(err)

    // approve mfa with totp
    mfaVoteTotpParams := models.MfaVoteTotpParams{
        MfaVote: ref.Of(models.Approve),
    }
    totpApproveRequest := models.TotpApproveRequest{
        Code: totpCode,
    }
    mfaTotpResp, err := oidcClient.MfaVoteTotp(totpResetResp.MfaRequired.Id, &mfaVoteTotpParams, totpApproveRequest)
    assertNil(err)

    // resubmit with MfaReceipt
    totpResetResp, err = oidcClient.UserResetTotpInit(nil, client.GetReceipt(mfaTotpResp))
    assert(err == nil && !totpResetResp.RequiresMfa())
}

The response contains a TOTP challenge, i.e., a new TOTP configuration in the form of the standard TOTP url. From that url, we can generate a QR code to present to the user, or create an authenticator for automated testing.

totpChallengeId := totpResetResp.ResponseData.TotpId
totpChallengeUrl := totpResetResp.ResponseData.TotpUrl
assert(totpChallengeUrl != "" && totpChallengeId != "")

To complete the challenge, we must call UserResetTotpComplete and provide the TOTP code matching the TOTP configuration from the challenge:

parsedUrl, _ := url.Parse(totpChallengeUrl)
urlParams, _ := url.ParseQuery(parsedUrl.RawQuery)
totpSecret = urlParams["secret"][0]

newTotpCode, err := totp.GenerateCode(totpSecret, time.Now())
assertNil(err)

totpChallengeAnswer := models.TotpChallengeAnswer {
    Code: newTotpCode,
    TotpId: totpChallengeId,
}
_, err = oidcClient.UserResetTotpComplete(totpChallengeAnswer)
assertNil(err)

After TOTP is configured, we can double check that our authenticator is generating the correct code by calling UserVerifyTotp

fmt.Println("Verifying current TOTP code")
totpCode, err := totp.GenerateCode(totpSecret, time.Now())
assertNil(err)

_, err = oidcClient.UserVerifyTotp(models.TotpApproveRequest{Code: totpCode})
assertNil(err)

We can also check that the user's profile now indeed includes Totp as one of the configured MFA factors.

userInfo, err = oidcClient.AboutMe()
assertNil(err)

foundTotp := false
for _, configuredMfa := range userInfo.Mfa {
    totpMfa, err := configuredMfa.AsConfiguredMfaTotp()
    assertNil(err)
    if totpMfa.Type == "totp" {
        foundTotp = true
    }
}

assert(foundTotp)

Configure MFA policy for signing

We've already discussed assigning a security policy to a key; requiring multi-factor authentication is another such policy.

Let's update our secpKey key to require an additional approval via TOTP before anything may be signed with that key:

fmt.Printf("Require Totp for key %s\n", secpKey.MaterialId)

// append current policy to require Mfa
newPolicy := append(secpKey.Policy, client.RequireMfaPolicy{RequireMfa: &models.MfaPolicy{
    Count: ref.Of(int32(1)),
    AllowedMfaTypes: ref.Of([]models.MfaType{client.TotpMfaType()}),
}})

_, err = apiClient.UpdateKey(secpKey.KeyId, models.UpdateKeyRequest{Policy: &newPolicy})
assertNil(err)

Now, when we call any signing operation on secpKey, we'll receive 202 Accepted instead of 200 Ok. The response body contains an MFA ID, which we can use to fetch and inspect the associated MFA request, see how many approvals it requires, what kind of MFA factors it allows, etc. Instead, since we know that our key requires TOTP, we can just call MfaVoteTotp on the response and pass the current TOTP code to it; if the code is correct, the call will succeed and return updated MfaRequestInfo. We then call client.GetReceipt to check if the approval was successful. With the MfaReceipt we can resubmit the original request to get the signature.

fmt.Println("Signing a transaction now requires TOTP")

eth1Resp, err = oidcClient.EvmSign(secpKey.MaterialId, eth1Request)
assert(err == nil && eth1Resp.RequiresMfa())

// approve request
totpCode, err = totp.GenerateCode(totpSecret, time.Now())
assertNil(err)

params := models.MfaVoteTotpParams{
    MfaVote: ref.Of(models.Approve),
}
approveRequest := models.TotpApproveRequest{
    Code: totpCode,
}
mfaTotpResp, err := oidcClient.MfaVoteTotp(eth1Resp.MfaRequired.Id, &params, approveRequest)
assert(err == nil && client.GetReceipt(mfaTotpResp) != nil)

// resubmit with receipt
eth1Resp, err = oidcClient.EvmSign(secpKey.MaterialId, eth1Request, client.GetReceipt(mfaTotpResp))
assert(err == nil && !eth1Resp.RequiresMfa() && eth1Resp.ResponseData.RlpSignedTx != "")

Clean up

Once we are done, we can revoke the sessions and delete the keys we created.

fmt.Println("Cleaning up")

// clean up signing session
_, err = signingClient.RevokeCurrentSession()
assertNil(err)

// clean up role session
_, err = roleClient.RevokeCurrentSession()
assertNil(err)

// clean up oidc session
_, err = oidcClient.RevokeCurrentSession()
assertNil(err)

// clean up role
_, err = apiClient.DeleteRole(roleResp.RoleId)
assertNil(err)

// Delete keys
deleteResp, err := apiClient.DeleteKey(secpKey.KeyId)
assertNil(err)

if deleteResp.RequiresMfa() {
    totpCode, err = totp.GenerateCode(totpSecret, time.Now())
    assertNil(err)

    params := models.MfaVoteTotpParams{MfaVote: ref.Of(models.Approve)}
    totpApproveRequest := models.TotpApproveRequest{Code: totpCode}
    mfaTotpResp, err = apiClient.MfaVoteTotp(deleteResp.MfaRequired.Id, &params, totpApproveRequest)
    assert(err == nil && client.GetReceipt(mfaTotpResp) != nil)

    // resubmit
    deleteResp, err := apiClient.DeleteKey(secpKey.KeyId, client.GetReceipt(mfaTotpResp))
    assert(err == nil && !deleteResp.RequiresMfa())

}

// Delete EdKey
_, err = apiClient.DeleteKey(edKey.KeyId)
assertNil(err)

Running the SDK tests

After logging in and setting the OIDC_TOKEN environment variable, you can just run:

make tests

Tests in tests/interactive_test.go are interactive test and must be compiled and run separately:

go test -c ./... -v # compiles all tests.
./test.test -test.run TestMfaSignEmail # runs TestMfaSignEmail

User input, e.g., Email Otp is needed for these tests and must be provided by the user in the CLI.