  The protection of confidential information is a global issue and block
encryption algorithms are the most reliable option. The famous information
theorist, Claude Shannon has given two desirable characteristics that should
exist in a strong cipher which are substitution and permutation in their
fundamental research on Communication Theory of Secrecy Systems. block ciphers
strictly follow the substitution and permutation principle to generate a
ciphertext. The actual strength of the block ciphers against several attacks is
entirely based on its substitution characteristic, which is gained by using the
S-Box. In the current literature, algebraic structure-based and chaos-based
techniques are highly used for the construction of S-boxes because both these
techniques have favourable features for S-box construction, but also various
attacks of these techniques have been identified. True randomness has been
universally recognized as the ideal method for cipher primitives design because
true random numbers are unpredictable, irreversible, and unreproducible. The
basic concept of the proposed technique is the extraction of true random bits
from underwater acoustic waves and to design a novel technique for the dynamic
generation of S-boxes using the chain of knights tour. The proposed method
satisfies all standard evaluation tests of S-boxes construction and true random
numbers generation. Two million bits have been analyzed using the NIST
randomness test suite, and the results show that underwater sound waves are an
impeccable entropy source for true randomness. Additionally, our dynamically
generated S-boxes have better or equal strength, over the latest published
S-boxes (2020 to 2021). According to our knowledge first time, this type of
research has been done, in which natural randomness of underwater acoustic
waves has been used for the construction of block cipher's S-Box
