Which property ensures that a hash function will not produce the same hashed value for two different messages?

Collision resistance means it is computationally infeasible to find any two different inputs M1 and M2 such that H(M1) equals H(M2). This property is critical for cryptographic integrity because a hash function that allows collisions can be exploited to substitute malicious data while preserving the original hash value, undermining authentication and digital signatures.

Bit length refers to the size of the hash output (e.g., 256 bits for SHA-256), which affects the security margin but does not itself define or guarantee collision resistance.

Key strength is a concept from symmetric and asymmetric encryption that describes key size and randomness; standard hash functions do not use keys and this term does not apply to the collision property.

Entropy measures the unpredictability or randomness of data and is relevant to key generation and password analysis, but it does not describe the specific property preventing two messages from mapping to the same hash value.