🚀 go-pugleaf

I've been hacking together a little program that does encryption using
one or more of DES, Triple DES, and IDEA.  I've come up with some
questions that I hope can be answered by the net.

1.  My understanding is that "Triple DES" is encryption using one
    key, decryption using another, then re-encryption using the
    first key.  Is this correct?  i.e., E3(P,K) = E(D(E(P,K1),K2),K1)

2.  Has triple DES actually been proven to be stronger than a single
    DES encryption?  I guess this boils down to whether DES has been
    proven to be a group.

3.  I've been using MD5 to hash an arbitary user-entered string into
    a key for the encryption process.  Is MD5 really suitable for the
    task?  It appears to be a particularly good hash for long strings
    of text, but is it suitable for short password-length text?

4.  In order to provide fast user-feedback if an incorrect decryption
    key is entered, I'm storing a "checksum" of the first block of
    plaintext in the encrypted file.  I was originally using a
    simple checksum, but that might give away too much information
    about the first block.  Now I apply MD5 to the block and take
    a byte of the message digest as the check digit.  Is this
    reasonable or would it be better to simply use the first
    8 bytes of the file as a DES/IDEA key to encrypt a constant and store
    a byte of that constant?

5.  Which is stronger, CBC or CFB?  Is one preferred over the other in
    cases where byte-per-byte output isn't important?

Thanks for any help!

Bill
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