Several types of keys can be used in crypto.  Arrays of bits, often
grouped as hexadecimal digits are quite common in contemoporary
algorithms but permutations of alphabets are common in classical
algorithms.  Alphabet loops or even arrays of loops are also used as
keys. There are still other types of keys but they are not the
emphasis of this posting.

Simple permutations have equivalent bit strengths and the values
presented are based on actual progressive decisions in their
generation.  Aside from how the permutation is effectively used, good,
bad, or somewhere in between, permutation keys can pack quite a
potential punch for the number of characters used. A loop permutation
is the same as for a regular permutation of one size smaller; for
example, a regular permutation key for base 26 would be equivalent to
about 97.94 bits or 61.80 trits but these values would be the same for
a base 27 loop.

Here are examples of loop permutations for a selected bases: base 10 =
21.79 bits; base 26 = 88.38 bits; base 40 = 159.16 bits; base 65 =
302.02 bits; base 78 = 382.2 bits; base 93 is 478.57 bits; and base 99
is 518.12 bits.

Often classical algorithms may use simple permutations in weaker
substitution schemes, modern character systems can use permutations
more effectively.  With loops or wheels in cylinders, multiply the
strength of one loop (or wheel) by the number of alphabets in the
cylinder.

Just having lots of keyspace is no excuse for not maximizing its use.
Classical algorithms tend to be poor, all but transparent in many
cases, but the better qualities in them are worth study so the best
primatives can be combined with newer ideas and extended into more
powerful systems.