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rsa.go
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rsa.go
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package keyfunc
import (
"crypto/rsa"
"encoding/base64"
"fmt"
"math/big"
)
const (
// rs256 represents a public cryptography key generated by a 256 bit RSA algorithm.
rs256 = "RS256"
// rs384 represents a public cryptography key generated by a 384 bit RSA algorithm.
rs384 = "RS384"
// rs512 represents a public cryptography key generated by a 512 bit RSA algorithm.
rs512 = "RS512"
// ps256 represents a public cryptography key generated by a 256 bit RSA algorithm.
ps256 = "PS256"
// ps384 represents a public cryptography key generated by a 384 bit RSA algorithm.
ps384 = "PS384"
// ps512 represents a public cryptography key generated by a 512 bit RSA algorithm.
ps512 = "PS512"
)
// RSA parses a JSONKey and turns it into an RSA public key.
func (j *JSONKey) RSA() (publicKey *rsa.PublicKey, err error) {
// Check if the key has already been computed.
if j.precomputed != nil {
return j.precomputed.(*rsa.PublicKey), nil
}
// Confirm everything needed is present.
if j.Exponent == "" || j.Modulus == "" {
return nil, fmt.Errorf("%w: rsa", ErrMissingAssets)
}
// Decode the exponent from Base64.
//
// According to RFC 7518, this is a Base64 URL unsigned integer.
// https://tools.ietf.org/html/rfc7518#section-6.3
var exponent []byte
if exponent, err = base64.RawURLEncoding.DecodeString(j.Exponent); err != nil {
return nil, err
}
// Decode the modulus from Base64.
var modulus []byte
if modulus, err = base64.RawURLEncoding.DecodeString(j.Modulus); err != nil {
return nil, err
}
// Create the RSA public key.
publicKey = &rsa.PublicKey{}
// Turn the exponent into an integer.
//
// According to RFC 7517, these numbers are in big-endian format.
// https://tools.ietf.org/html/rfc7517#appendix-A.1
publicKey.E = int(big.NewInt(0).SetBytes(exponent).Uint64())
// Turn the modulus into a *big.Int.
publicKey.N = big.NewInt(0).SetBytes(modulus)
// Keep the public key so it won't have to be computed every time.
j.precomputed = publicKey
return publicKey, nil
}