The TETRA TA61 identity encryption function internally uses a 64-bit value derived exclusively from the SCK (Class 2 networks) or CCK (Class 3 networks). The structure of TA61 allows for efficient recovery of this 64-bit value, allowing an adversary to encrypt or decrypt arbitrary identities given only three known encrypted/unencrypted identity pairs.

The TETRA TA61 identity encryption function internally uses a 64-bit value derived exclusively from the SCK (Class 2 networks) or CCK (Class 3 networks). The structure of TA61 allows for efficient recovery of this 64-bit value, allowing an adversary to encrypt or decrypt arbitrary identities given only three known encrypted/unencrypted identity pairs.