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Lab7.md

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Encryption and Decryption

  1. Decrypt file1.txt.gpg with the password ocfdecal (for real-life purposes, never store passwords in plaintext). What are the decrypted contents of file1.txt.gpg? Answer: Quack echo "ocfdecal" | gpg --batch --passphrase-fd 0 --decrypt file1.txt.gpg `gpg --batch --passphrase ocfdecal --decrypt file1.txt.gpg --batch: Use batch mode. Never ask, do not allow interactive commands. --passphrase-fd n : Read the passphrase from file descriptor n. If you use 0 for n, the passphrase will be read from stdin. This can only be used if only one passphrase is supplied. Don't use this option if you can avoid it.
  2. What command allows you to import a key? --import [_files_], --fast-import [_files_]: Import/merge keys. This adds the given keys to the keyring. The fast version does not build the trustdb; this can be done at any time with the command --update-trustdb
  3. What command allows you to export a key to a file? (Add the --armor flag to ASCII-encode the key so it can be sent easily in text form) --export [_names_]: Either export all keys from all keyrings (default keyrings and those registered via option --keyring), or if at least one name is given, those of the given name. The new keyring is written to stdout or to the file given with option "output". Use together with --armor to mail those keys.

4. What command allows you to see all of the keys on your keyring? `--list-keys [_names_], --list-public-keys [_names_]`: List all keys from the public keyrings, or just the ones given on the command line. `--list-secret-keys [_names_]`: List all keys from the secret keyrings, or just the ones given on the command line.
6. Use the private key `lab7privkey` to decrypt the file `file2.txt.gpg` (_for real-life purposes, it is necessary to keep private keys secret_). What are the decrypted contents of `b8/file2.txt.gpg`? ``` $ gpg --import "lab7privkey" gpg: key 82DDDAA6869E6CEC: public key "lab7privkey" imported gpg: key 82DDDAA6869E6CEC: secret key imported gpg: Total number processed: 1 gpg: imported: 1 gpg: secret keys read: 1 gpg: secret keys imported: 1 $ gpg --decrypt file2.txt.gpg gpg: Note: secret key 83ADADD521C1D38D expired at Tue 31 Oct 2023 07:00:00 PM UTC gpg: encrypted with 2048-bit RSA key, ID 83ADADD521C1D38D, created 2018-10-31 "lab7privkey" Woof ``` (But "lab7privkey" is a private key I don't know why it contained as a public key) And the decrypted contents of b8/file2.txt: Woof
### Hashing (Checksums)
  1. What is the MD5 hash of file3.txt? 
    $ md5sum file3.txt
ddbefc9c1d8a8d9195a420a7181352e9  file3.txt
  2. What is the SHA1 hash of the MD5 hash of file3.txt? In other words, what is SHA1(MD5(file3.txt))? 
    $ echo "ddbefc9c1d8a8d9195a420a7181352e9" | sha1sum
15c3d7fa41fcc2ed98c2fda065e3248047a048f4  -
    • Incorrect command: md5sum file3.txt > a.txt | sha1sum (can't use "|" after ">")
    • correct command but incorrect output: md5sum file3.txt | sha1sum (It output the SHA1 hash of the MD5 hash of file3.txt + file3.txt)

File Security

Run sudo setup.sh before beginning this section.

  1. file4.txt: What are the permissions of this file? Explain what they allow and disallow. -rw-r--r-- 1 nobody lucus 15 Feb 3 07:04 file4.txt -: this is a file rw-: readable and writable for "nobody" r--r--: read only for group and other 1: indicates the number of hard links to the file nobody: user owner of the file lucus: group owner of the file 15: file size in bytes Feb 3 07:04: last modification timestamp of the file
  2. file5: Make this file executable and execute it. What is its printout? 
    $ chmod +x file5
$ ./file5
-bash: ./file5: cannot execute binary file: Exec format error
$ file file5
file5: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically      linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32,           BuildID[sha1]=fba4dfb4c3e61e810339d350b131607d5c76d3a1, not stripped
$ uname -m
aarch64
    Unfortunately:(
  3. file6.txt: Change this file to be under your ownership. What command did you use? $ sudo chown lucus:lucus file6.txt
  4. file7.txt: Make this file readable only to you. What command did you use? $ sudo chown lucus:lucus file7.txt
  5. file8.txt: Change this file’s permissions such that only root should be able to read this file and no one should be able to edit it. What command did you use? sudo chown root:root file8.txt sudo chmod 511 file8.txt(r:4;w:2;x:1) -r-x--x--x 1 root root 20 Feb 3 07:25 file8.txt
  6. file9.txt: Choose any method to make this file readable to you and unreadable to the previous owner. What command did you use?
$ sudo groupadd developers
$ sudo usermod -aG developers lucus
$ sudo chown lucus:developers file9.txt
$ chmod o-r file9.txt
$ ls -l
...
-rwxrwx-wx 1 lucus  developers   19 Feb  3 07:25 file9.txt

There will make the file readable to other users while ensuring the previous owner has no access. (add other users except the previous user into the specific group)