tinyssh/tools/tinyssh-convert at master · janmojzis/tinyssh · GitHub

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#!/usr/bin/env python3

import os
import sys
import base64
import struct


"""
        byte[]        AUTH_MAGIC = "openssh-key-v1\x00"
        string        ciphername
        string        kdfname
        string        kdfoptions
        int        number of keys N
        string        publickey1
        string        publickey2
        ...
        string        publickeyN
        string        encrypted, padded list of private keys
"""

class Parser:
        """
        """

        def __init__(self, data = b""):
                """
                """

                self.data = data

        def parse_magic(self):
                """
                """

                if len(self.data) < 15 or not self.data.startswith(b"openssh-key-v1\x00"):
                        raise Exception("unable to parse OpenSSH key: magic 'openssh-key-v1' not found")
                self.data = self.data[15:]

        def parse_num(self, text):
                """
                """

                if (4 > len(self.data)):
                        raise Exception(f"unable to parse OpenSSH key: bad ssh-num {text}")

                num = struct.unpack('>I', self.data[:4])[0]
                self.data = self.data[4:]
                return num

        def parse_string(self, text):
                """
                """

                num = self.parse_num(text)

                if (num > len(self.data)):
                        raise Exception(f"unable to parse OpenSSH key: bad ssh-string {text}")

                ret = self.data[:num]
                self.data = self.data[num:]
                return ret

def usage(f = ""):
        """
        """

        if len(f) != 0:
                print("tinyssh-convert: fatal: %s" % (f))
        print("tinyssh-convert: usage: tinyssh-convert out-tinysshkeydir < in-opensshfile")
        print()
        exit(100)

def writesync(fn = "", data = b""):
        """
        """

        f = open(fn, 'wb')
        f.write(data)
        f.flush()
        os.fsync(f.fileno())
        f.close()


if __name__ == "__main__":

        if len(sys.argv) != 2:
                usage("")
        d=sys.argv[1]

        if os.path.exists(d):
                usage("out-tinysshkeydir exist")

        lines = sys.stdin.readlines()
        data = ""
        flagbegin = 0
        for line in lines:
                if line.startswith("-----BEGIN OPENSSH PRIVATE KEY-----"):
                        flagbegin = 1
                        continue
                if line.startswith("-----END OPENSSH PRIVATE KEY-----"):
                        break
                if flagbegin:
                        data += line

        if flagbegin == 0:
                raise Exception("unable to parse OpenSSH key: no line -----BEGIN OPENSSH PRIVATE KEY----- found")

        data = base64.b64decode(data)

        # parse key
        p = Parser(data)
        p.parse_magic()
        ciphername = p.parse_string("ciphername")
        if ciphername != b'none':
                raise Exception("unable to parse OpenSSH key: can't convert encrypted key: ciphername != none")
        kdfname = p.parse_string("kdfname")
        if kdfname != b'none':
                raise Exception("unable to parse OpenSSH key: can't convert encrypted key: kdfname != none")
        kdfoptions = p.parse_string("kdfoptions")
        if kdfoptions != b'':
                raise Exception("unable to parse OpenSSH key: can't convert encrypted key: kdfoptions != ''")
        pklen = p.parse_num("publickeys")
        if (pklen != 1):
                raise Exception("unable to parse OpenSSH key: more than one key in the file")

        pkssh = p.parse_string("publickey")
        skssh = p.parse_string("secretkeys")

        # parse secret key
        p = Parser(skssh)
        p.parse_num("checkint")
        p.parse_num("checkint")
        sk = []
        t = p.parse_string("secret-key type")
        if t != b'ssh-ed25519':
                raise Exception(f"unable to parse OpenSSH key: secret-key type={t}: not ssh-ed25519 key")
        pk = p.parse_string("public-key")
        pklen = len(pk)
        sk = p.parse_string("secret-key")
        sklen = len(sk)
        p.parse_string("comment")
        if pklen != 32:
                raise Exception(f"unable to parse OpenSSH key: public-key length={pklen}: not 32")
        if sklen != 64:
                raise Exception(f"unable to parse OpenSSH key: secret-key length={sklen}: not 64")

        os.umask(0o0022)
        os.mkdir(d)
        os.chdir(d)
        writesync("ed25519.pk", pk)
        os.umask(0o0077)
        writesync(".ed25519.sk", sk)