- markus@cvs.openbsd.org 2013/12/06 13:34:54
[authfile.c authfile.h cipher.c cipher.h key.c packet.c ssh-agent.c]
[ssh-keygen.c PROTOCOL.key] new private key format, bcrypt as KDF by
default; details in PROTOCOL.key; feedback and lots help from djm;
ok djm@
diff --git a/PROTOCOL.key b/PROTOCOL.key
new file mode 100644
index 0000000..959bd7a
--- /dev/null
+++ b/PROTOCOL.key
@@ -0,0 +1,68 @@
+This document describes the private key format for OpenSSH.
+
+1. Overall format
+
+The key consists of a header, a list of public keys, and
+an encrypted list of matching private keys.
+
+#define AUTH_MAGIC "openssh-key-v1"
+
+ byte[] AUTH_MAGIC
+ string ciphername
+ string kdfname
+ string kdfoptions
+ int number of keys N
+ string publickey1
+ string publickey2
+ ...
+ string publickeyN
+ string encrypted, padded list of private keys
+
+2. KDF options for kdfname "bcrypt"
+
+The options:
+
+ string salt
+ uint32 rounds
+
+are concatenated and represented as a string.
+
+3. Unencrypted list of N private keys
+
+The list of privatekey/comment pairs is padded with the
+bytes 1, 2, 3, ... until the total length is a multiple
+of the cipher block size.
+
+ uint32 checkint
+ uint32 checkint
+ string privatekey1
+ string comment1
+ string privatekey2
+ string comment2
+ ...
+ string privatekeyN
+ string commentN
+ char 1
+ char 2
+ char 3
+ ...
+ char padlen % 255
+
+Before the key is encrypted, a random integer is assigned
+to both checkint fields so successful decryption can be
+quickly checked by verifying that both checkint fields
+hold the same value.
+
+4. Encryption
+
+The KDF is used to derive a key, IV (and other values required by
+the cipher) from the passphrase. These values are then used to
+encrypt the unencrypted list of private keys.
+
+5. No encryption
+
+For unencrypted keys the cipher "none" and the KDF "none"
+are used with empty passphrases. The options if the KDF "none"
+are the empty string.
+
+$OpenBSD: PROTOCOL.key,v 1.1 2013/12/06 13:34:54 markus Exp $