Explain the difference between CFB and OFB modes of block cipher operation. What mode is more reliable? Why?

Hints:

IV CM-1 Shift register 64-bits s bits Shift register 64-bits s bits Shift register 64-bits s bits 64 764 64 K-Encrypt 64 K-Encrypt 64 K-Encrypt 64 Select s bits Discard 64-bits Select s bits Discard 64-bits Select s bits Discord 64-bits P1 S P2 PM CM C2 (a) Encryption IV CM-1 Shift register 64-bits s bits Shift register 64-bits s bits Shift register 64-bits s bits 64 64 X64 Encrypt K K-Encrypt 64 K-Decrypt 64 64 Select /bits Discard 64-bits Select s bits Discard 64-bits Select s bits Discard 64 - 8 bits S S - PL PM P2 (b) Decryption Figure 3.13 s-bit Cipher Feedback (CFB) Mode IV OM-1 Shift register 64-bits Shift register 64-8 bits s bits s bits s bits 64 X64 Shift register 64-bits X64 Encrypt 64 Select Discard s bits 64-bits Encrypt 64 Encrypt 64 Select Discard s bits | 64-bits S Select s bits Discard 64-bits P S P2 PM S C2 (a) Encryption IV OM-1 Shift register 64-bits s bits Shift register 64-bits s bits Shift register 64-bits s bits 64 X64 Encrypt 64 Select Discard 64-bits K-Encrypt 64 Select Discard s bits 64-bits S Decrypt 64 Select Discard 64-bits bits s bits C -CM PM P2 (b) Decryption Figure 3.14 s-bit Output Feedback (OFB) Mode