crypto.Signer, implementations for Google Cloud KMS and Trusted Platform Modules

where private keys as embedded inside:

• Google Cloud KMS
• Trusted Platform Module (TPM)

Basically, you will get a crypto.Signer interface where the private keys are saved on those platform.

Use the signer to create a TLS session, sign CA/CSRs, generate signed url or just sign anything.

Some implementations:

• kms/: Sample that implements crypto.Signer using Google Cloud KMS.

• tpm/: Sample that implements crypto.Signer using go-tpm library for Trusted Platform Module This internally uses go-tpm-tools.client.GetSigner()

• util/certgen/: Library that generates a self-signed x509 certificate for the KMS and TPM based signers above

• util/csrgen/: Library that generates a CSR using the key in KMS or TPM

see the example/ folder for more information.

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this library is not supported by google

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Usage Signer

Initialize a signer and directly use .sign() as shown in this sample for GCS SignedURL:

• GCS SignedURL for KMS
• GCS signedURLs and GCP Authentication with Trusted Platform Module

Usage TLS

• for tpm see mTLS with TPM bound private key
• for kms see mTLS with Google Cloud KMS

Sign/Verify PSS

see example/sign_verify* folders

Sign/Verify ECC

The default output signature format for ECC based keys is ASN1 format as described in ecdsa.SignASN1

If you need the raw output format, set ECCRawOutput: true in the config.

See the examples folder for usage

Usage: Generate self-signed certificate

see util/

go run certgen/certgen.go -cn server.domain.com

Usage: Generate CSR

see util/csrgen/

go run certgen/certgen.go -cn server.domain.com

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If you just want to issue JWT's, see

• https://github.com/salrashid123/golang-jwt-tpm
• https://github.com/salrashid123/golang-jwt-pkcs11

TPM Signer Device management

NOTE there will be a breaking change if you are using this library for TPM based signature after v0.8.0. The new structure uses the tpm-direct API. If you would rather use the tpm2/legacy branch, please use the signer at v0.7.2. Library managed device was removed (it seems tpm resource managers work well enough...I'm clearly on the fence here given the recent commits..)

The TPM device is managed externally outside of the signer. You have to instantiate the TPM device ReadWriteCloser and client.Key outside of the library and pass that in.

The advantage of this is you control it opening and closing. You must close the key and closer before calling another signing operation.

  rwc, err := OpenTPM(*tpmPath)
  rwr := transport.FromReadWriter(rwc)

  pub, err := tpm2.ReadPublic{
  	ObjectHandle: tpm2.TPMHandle(*handle),
  }.Execute(rwr)

  r, err := saltpm.NewTPMCrypto(&saltpm.TPM{
  	TpmDevice: rwc,
  	NamedHandle: &tpm2.NamedHandle{
  		Handle: tpm2.TPMHandle(*handle),
  		Name:   pub.Name,
  	},
  })
  // the tpm is opened and then closed after every sign operation
  s, err := r.Sign(rand.Reader, digest, crypto.SHA256)

TODO use a backoff retry similar to tpmrand to prevent contention.