cryptokms

Implements crypto.Signer and crypto.Decrypter for keys typically backed by KMS service. Currently it supports keys backed by,

• Google Cloud KMS
• AWS KMS
• Filesystem
• From memory.

Dependencies are neatly isolated. If you pull gcpkms package only google cloud dependencies should be pulled. Code has extensive unit tests and integration tests.

Uses sensible and sane defaults.

• RSA keys of size less than 2048 are not supported.
• ECC Keys of size less than 256 are not supported.
• Signing algorithms with insecure hashes (SHA1, MD5 etc) are not supported.

Google KMS (Signing Keys)

Key Algorithm	Hash Algorithm	Supported Interfaces
EC_SIGN_P256_SHA256(recommended)	sha256	crypto.Signer, crypto.SignerOpts
EC_SIGN_P384_SHA384	sha384	crypto.Signer, crypto.SignerOpts
RSA_SIGN_PKCS1_2048_SHA256	sha256	crypto.Signer, crypto.SignerOpts
RSA_SIGN_PKCS1_3072_SHA256	sha256	crypto.Signer, crypto.SignerOpts
RSA_SIGN_PKCS1_4096_SHA256	sha256	crypto.Signer, crypto.SignerOpts
RSA_SIGN_PKCS1_4096_SHA512	sha512	crypto.Signer, crypto.SignerOpts

Important

RSA_SIGN_PSS_*, RSA_SIGN_RAW_* and external KMS keys are not supported.

Google KMS (Encryption Keys)

Key Algorithm	Hash Algorithm	Supported Interfaces
RSA_DECRYPT_OAEP_2048_SHA1	sha1	crypto.Decrypter
RSA_DECRYPT_OAEP_3072_SHA1	sha1	crypto.Decrypter
RSA_DECRYPT_OAEP_4096_SHA1	sha1	crypto.Decrypter
RSA_DECRYPT_OAEP_2048_SHA256	sha256	crypto.Decrypter
RSA_DECRYPT_OAEP_3072_SHA256(recommended)	sha256	crypto.Decrypter
RSA_DECRYPT_OAEP_4096_SHA256	sha256	crypto.Decrypter
RSA_DECRYPT_OAEP_4096_SHA512	sha512	crypto.Decrypter

AWS KMS (Signing Keys)

Key Algorithm	Key Usage	Hash Algorithm	Supported Interfaces
RSA_2048	SIGN_VERIFY	sha256, sha384, sha512	crypto.Signer, crypto.SignerOpts
RSA_3072	SIGN_VERIFY	sha256, sha384, sha512	crypto.Signer, crypto.SignerOpts
RSA_4096	SIGN_VERIFY	sha256, sha384, sha512	crypto.Signer, crypto.SignerOpts
ECC_NIST_P256(recommended)	SIGN_VERIFY	sha256	crypto.Signer, crypto.SignerOpts
ECC_NIST_384	SIGN_VERIFY	sha384	crypto.Signer, crypto.SignerOpts
ECC_NIST_P521	SIGN_VERIFY	sha512	crypto.Signer, crypto.SignerOpts

AWS KMS (Encryption Keys)

Key Algorithm	Key Usage	Encryption Algorithms	Supported Interfaces
RSA_2048	ENCRYPT_DECRYPT	RSAES_OAEP_SHA_1,RSAES_OAEP_SHA_256	crypto.Decrypter
RSA_3072	ENCRYPT_DECRYPT	RSAES_OAEP_SHA_1,RSAES_OAEP_SHA_256	crypto.Decrypter
RSA_4096	ENCRYPT_DECRYPT	RSAES_OAEP_SHA_1,RSAES_OAEP_SHA_256	crypto.Decrypter

Keys from filesystem

Important

Use in-memory non swap-able file system (like ramfs) or from kubernetes secret store CSI. For systems using systemd, systemd-credentials can be used as keys can be encrypted, bound to TPM and are only present in memory. In other cases this may be insecure.

Keys on disk must be not encrypted with a passphrase. Private key in PKCS #8, ASN.1 DER form(PRIVATE KEY), RSA private key in PKCS #1, ASN.1 DER form(RSA PRIVATE KEY) and EC private key in SEC 1, ASN.1 DER form (EC PRIVATE KEY) are supported.

Key Algorithm	Supported Hashes	Interfaces
RSA_2048	SHA1, SHA256, SHA512	crypto.Decrypter, crypto.Signer
RSA_3072	SHA1, SHA256, SHA512	crypto.Decrypter, crypto.Signer
RSA_4096	SHA1, SHA256, SHA512	crypto.Decrypter, crypto.Signer
ECC-P256	SHA256	crypto.Signer
ECC-P384	SHA384	crypto.Signer
ECC-P521	SHA512	crypto.Signer
ED-25519	SHA512 (ed25519ph only)	crypto.Signer

From memory

If keys are stored in memory or environment variables, use memkms. It is identical to filekms except keys are in-process and are provided directly. Key must be PEM encoded.