DES has been specified to take a 64 bit key, but only 56 of them are used. The remainder are parity bits.

The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits

For 3DES the nominal key size is $3 \cdot 64 = 192$ bits and $3 \cdot 56 = 168$ of them are used.

The 3DES construction suffers from a meet-in-the-middle attack, which reduces the cost of breaking it to about $2^{112}$ operations, leading to an effective security of 112 bits.

DES has been specified to take a 64 bit key, but only 56 of them are used. The remainder are parity bits.

The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits

For 3DES the nominal key size is $3 \cdot 64 = 192$ bits and $3 \cdot 56 = 168$ of them are used.

The 3DES construction suffers from a meet-in-the-middle attack, which reduces the cost of breaking it to about $2^{112}$ operations, leading to an effective security of 112 bits.

DES has been specified to take a 64 bit key, but only 56 of them are used. The remainder are parity bits. So the nominal key size is $3 \cdot 64 = 192$ bits for 3DES, and $3 \cdot 56 = 168$ of them are used.

The 3DES construction suffers from a meet-in-the-middle attack, which reduces the cost of breaking it to about $2^{112}$ operations, leading to an effective security of 112 bits.

DES has been specified to take a 64 bit key, but only 56 of them are used. The remainder are parity bits.

The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits

For 3DES the nominal key size is $3 \cdot 64 = 192$ bits and $3 \cdot 56 = 168$ of them are used.

The 3DES construction suffers from a meet-in-the-middle attack, which reduces the cost of breaking it to about $2^{112}$ operations, leading to an effective security of 112 bits.