| 1 | package crypto |
| 2 | |
| 3 | import ( |
| 4 | "crypto/rand" |
| 5 | "crypto/rsa" |
| 6 | "crypto/sha1" |
| 7 | "crypto/sha256" |
| 8 | "crypto/x509" |
| 9 | "fmt" |
| 10 | "hash" |
| 11 | ) |
| 12 | |
| 13 | // DecryptRSA decrypts a CipherString using an RSA private key. |
| 14 | func DecryptRSA(cs *CipherString, privKey *rsa.PrivateKey) ([]byte, error) { |
| 15 | var h hash.Hash |
| 16 | switch cs.Type { |
| 17 | case EncRsa2048_OaepSha1_B64, EncRsa2048_OaepSha1_HmacSha256_B64: |
| 18 | h = sha1.New() |
| 19 | case EncRsa2048_OaepSha256_B64, EncRsa2048_OaepSha256_HmacSha256_B64: |
| 20 | h = sha256.New() |
| 21 | default: |
| 22 | return nil, fmt.Errorf("not an RSA cipher string type: %d", cs.Type) |
| 23 | } |
| 24 | |
| 25 | plaintext, err := rsa.DecryptOAEP(h, rand.Reader, privKey, cs.CT, nil) |
| 26 | if err != nil { |
| 27 | return nil, fmt.Errorf("RSA decrypt: %w", err) |
| 28 | } |
| 29 | return plaintext, nil |
| 30 | } |
| 31 | |
| 32 | // EncryptRSA encrypts plaintext with an RSA public key using OAEP-SHA1 (type 4). |
| 33 | func EncryptRSA(plaintext []byte, pubKey *rsa.PublicKey) (*CipherString, error) { |
| 34 | ct, err := rsa.EncryptOAEP(sha1.New(), rand.Reader, pubKey, plaintext, nil) |
| 35 | if err != nil { |
| 36 | return nil, fmt.Errorf("RSA encrypt: %w", err) |
| 37 | } |
| 38 | return &CipherString{ |
| 39 | Type: EncRsa2048_OaepSha1_B64, |
| 40 | CT: ct, |
| 41 | }, nil |
| 42 | } |
| 43 | |
| 44 | // GenerateRSAKeyPair generates a 2048-bit RSA key pair. |
| 45 | func GenerateRSAKeyPair() (*rsa.PrivateKey, error) { |
| 46 | return rsa.GenerateKey(rand.Reader, 2048) |
| 47 | } |
| 48 | |
| 49 | // MarshalPrivateKey marshals an RSA private key to PKCS8 DER format. |
| 50 | func MarshalPrivateKey(key *rsa.PrivateKey) ([]byte, error) { |
| 51 | return x509.MarshalPKCS8PrivateKey(key) |
| 52 | } |
| 53 | |
| 54 | // MarshalPublicKey marshals an RSA public key to PKIX DER format. |
| 55 | func MarshalPublicKey(key *rsa.PublicKey) ([]byte, error) { |
| 56 | return x509.MarshalPKIXPublicKey(key) |
| 57 | } |
| 58 | |
| 59 | // ParsePrivateKey parses a PKCS8 DER-encoded RSA private key. |
| 60 | func ParsePrivateKey(der []byte) (*rsa.PrivateKey, error) { |
| 61 | key, err := x509.ParsePKCS8PrivateKey(der) |
| 62 | if err != nil { |
| 63 | return nil, fmt.Errorf("parse PKCS8 private key: %w", err) |
| 64 | } |
| 65 | rsaKey, ok := key.(*rsa.PrivateKey) |
| 66 | if !ok { |
| 67 | return nil, fmt.Errorf("not an RSA private key") |
| 68 | } |
| 69 | return rsaKey, nil |
| 70 | } |
| 71 | |