agessh: properly detect public key mismatch for encrypted keys

agessh/encrypted_keys.go

@@ -5,6 +5,7 @@
 package agessh
 
 import (
+	"crypto"
 	"crypto/ed25519"
 	"crypto/rsa"
 	"fmt"
@@ -105,19 +106,16 @@ func (i *EncryptedSSHIdentity) Unwrap(stanzas []*age.Stanza) (fileKey []byte, er
 		return nil, fmt.Errorf("failed to decrypt SSH key file: %v", err)
 	}
 
+	var pubKey interface {
+		Equal(x crypto.PublicKey) bool
+	}
 	switch k := k.(type) {
 	case *ed25519.PrivateKey:
 		i.decrypted, err = NewEd25519Identity(*k)
-		// TODO: here and below, better check that the two public keys match,
-		// rather than just the type.
-		if i.pubKey.Type() != ssh.KeyAlgoED25519 {
-			return nil, fmt.Errorf("mismatched private (%s) and public (%s) SSH key types", ssh.KeyAlgoED25519, i.pubKey.Type())
-		}
+		pubKey = k.Public().(ed25519.PublicKey)
 	case *rsa.PrivateKey:
 		i.decrypted, err = NewRSAIdentity(k)
-		if i.pubKey.Type() != ssh.KeyAlgoRSA {
-			return nil, fmt.Errorf("mismatched private (%s) and public (%s) SSH key types", ssh.KeyAlgoRSA, i.pubKey.Type())
-		}
+		pubKey = &k.PublicKey
 	default:
 		return nil, fmt.Errorf("unexpected SSH key type: %T", k)
 	}
@@ -125,5 +123,9 @@ func (i *EncryptedSSHIdentity) Unwrap(stanzas []*age.Stanza) (fileKey []byte, er
 		return nil, fmt.Errorf("invalid SSH key: %v", err)
 	}
 
+	if exp := i.pubKey.(ssh.CryptoPublicKey).CryptoPublicKey(); !pubKey.Equal(exp) {
+		return nil, fmt.Errorf("mismatched private and public SSH key")
+	}
+
 	return i.decrypted.Unwrap(stanzas)
 }

cmd/age/testdata/encrypted_keys.txt

@@ -0,0 +1,98 @@
+[windows] skip # no pty support
+
+# use an encrypted OpenSSH private key without .pub file
+age -R key_ed25519.pub -o ed25519.age input
+rm key_ed25519.pub
+pty terminal
+age -d -i key_ed25519 ed25519.age
+stdout test
+
+# a file encrypted to the wrong key does not ask for the password
+age -R key_ed25519_other.pub -o ed25519_other.age input
+! age -d -i key_ed25519 ed25519_other.age
+stderr 'no identity matched any of the recipients'
+
+# use an encrypted legacy PEM private key with a .pub file
+age -R key_rsa_legacy.pub -o rsa_legacy.age input
+pty terminal
+age -d -i key_rsa_legacy rsa_legacy.age
+stdout test
+age -R key_rsa_other.pub -o rsa_other.age input
+! age -d -i key_rsa_legacy rsa_other.age
+stderr 'no identity matched any of the recipients'
+
+# legacy PEM private key without a .pub file causes an error
+rm key_rsa_legacy.pub
+! age -d -i key_rsa_legacy rsa_legacy.age
+stderr 'key_rsa_legacy.pub'
+
+# mismatched .pub file causes an error
+cp key_rsa_legacy key_rsa_other
+pty terminal
+! age -d -i key_rsa_other rsa_other.age
+stderr 'mismatched private and public SSH key'
+
+-- input --
+test
+-- terminal --
+password
+-- key_ed25519 --
+-----BEGIN OPENSSH PRIVATE KEY-----
+b3BlbnNzaC1rZXktdjEAAAAACmFlczI1Ni1jdHIAAAAGYmNyeXB0AAAAGAAAABCuvb97i7
+U6Dz4+4SaF3kK1AAAAEAAAAAEAAAAzAAAAC3NzaC1lZDI1NTE5AAAAIKaVctg4/hmFbfof
+Tv+yrC2IweO/Dd2AVDijFpaMO9fmAAAAoMO7yEnisRmzFdiExNt3XTYuLdP9m3jgOCroiF
+TtBhh1lAB2qggzWExMRP3Ak8+AloXEcWiACwBYnqwxhQMh0RDCDKC/H/4SXO+ds4HFWil+
+4bGF9wYZFU7IEjIK91CPGJ6YoWPn9dSdEjjbuCJtOMwHsysGyw5n/qSFPmSAPmA4YL2OzM
+WFOJ5gB5o1LKZkDTcdt7kPziIoVd5QkqpnYsE=
+-----END OPENSSH PRIVATE KEY-----
+-- key_ed25519.pub --
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKaVctg4/hmFbfofTv+yrC2IweO/Dd2AVDijFpaMO9fm
+-- key_ed25519_other.pub --
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAINbTd+xfSBYKR/1Hp7FsoxwQAdIOk1Khye6ALBj7e1CV
+-- key_rsa_legacy --
+-----BEGIN RSA PRIVATE KEY-----
+Proc-Type: 4,ENCRYPTED
+DEK-Info: AES-128-CBC,8045E7CF19D7794F4ADF5AC63179D985
+
+OESHhWCho337W1Ajg+iMbsZx/FPtHM3YPHu/d1U51ERIUh0wVof2SK0ooENokr6g
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++6o0NXYCJNaeVnk1bE4iavkJrXJCZvu44VBLS0WUs9W8TD4Iq8kNHsfQsfOuBXnQ
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+Erm699vIBQwvv0i+mcwKEvqSrhhNQ2F7vrb7NL8I2wUEPgQbv1PxSV6X0aYcxYVI
+-----END RSA PRIVATE KEY-----
+-- key_rsa_legacy.pub --
+ssh-rsa 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
+-- key_rsa_other.pub --
+ssh-rsa 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

cmd/age/testdata/scrypt.txt

@@ -1,28 +1,28 @@
 [windows] skip # no pty support
 
-# Encrypt with a provided passphrase.
+# encrypt with a provided passphrase
 pty terminal
 age -p -o test.age
 ! stderr .
 ! stdout .
 
-# Decrypt with a provided passphrase.
+# decrypt with a provided passphrase
 pty terminal
 age -d test.age
 ! stderr .
 ! stdout .
 
-# Decrypt with the wrong passphrase.
+# decrypt with the wrong passphrase
 pty wrong
 ! age -d test.age
 stderr 'incorrect passphrase'
 
-# Fail when -i is present.
+# fail when -i is present
 pty terminal
 ! age -d -i key.txt test.age
 stderr 'file is passphrase-encrypted but identities were specified'
 
-# Fail when passphrases don't match.
+# fail when passphrases don't match
 pty wrong
 ! age -p -o fail.age
 stderr 'passphrases didn''t match'