How Can I Securely Save and Load RSA Private and Public Keys in Go?

Saving and Loading Private and Public Keys for RSA Encryption

When working with the crypto/rsa package in Go, it becomes necessary to store and retrieve private and public keys securely. This article provides comprehensive guidance on properly handling the task of persisting these keys to the disk and restoring them when needed.

Saving RSA Private Keys

To create a byte slice representing an rsa.PrivateKey, use the following function:

func x509.MarshalPKCS1PrivateKey(key *rsa.PrivateKey) []byte

This function marshals the private key into a byte slice following the PKCS#1 standard.

Saving RSA Public Keys

For rsa.PublicKey, there is no built-in function in the Go standard library to marshal the key into a byte slice. However, it is common practice to encode the marshaled private key into a PEM file using the following code:

pemdata := pem.EncodeToMemory(
    &pem.Block{
        Type: "RSA PRIVATE KEY",
        Bytes: x509.MarshalPKCS1PrivateKey(key),
    },
)

This code snippet wraps the marshaled private key in a PEM block and encodes it into a PEM-formatted byte slice.

Loading RSA Private and Public Keys

To load an RSA private key from a disk or memory, use the following function:

func x509.ParsePKCS1PrivateKey(der []byte) (key *rsa.PrivateKey, err error)

This function parses a DER-encoded private key byte slice and returns an rsa.PrivateKey object.

Since public keys do not have their own parsing function, you would need to extract the public key from the private key if you have both loaded. To extract the public key from a private key, use the following code:

pub := &key.PublicKey

Conclusion

This comprehensive guide provides the necessary information and functions for securely saving and loading RSA private and public keys in Go, ensuring proper management and accessibility of these keys for cryptographic operations.

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