I'm learning how CBC works but i don't understand when altering the first 2 bytes of the ciphered text why the 1rst block and ONLY the first 2 bytes of the second block are altered. The first 2 bytes of the cypher text are altered using a xor operation with random values. Each block is made of 16 bytes.
Those are the random bytes to encrypt:
D6 D7 17 2B D8 1B 73 DF AA D4 D0 DC 94 D1 C2 B2 EE 0D 3B DA 74 58 62 F9 F9 D1 30 59 F5 FE 7D 54 14 79 42 14 B6 1D 34 C7 19 B0 68 67 36 25 D9 FA D0 1C 61 CB 40 A2 CD 77 6A 7D D3 D4 A2 23 9B 4F AF
This is the cypher text:
D2 CD F5 92 8D 1D 4E BC A1 9A CE 50 07 8C 13 FE 33 4B FE BD A0 6B 6C 7B F4 38 90 F4 36 A6 9A 15 A3 D8 41 F4 04 5D C0 9C A3 B6 A6 A8 4A B5 B2 F9 3C E3 0B 93 5E E1 42 26 66 58 16 39 A4 9C 14 5D 69 E9 EE C8 7D 0F AC 85 E7 EC 9C 0B C4 E4 74 22
This is the altered cypher text by xoring the previous text with 80 80:
52 4D F5 92 8D 1D 4E BC A1 9A CE 50 07 8C 13 FE 33 4B FE BD A0 6B 6C 7B F4 38 90 F4 36 A6 9A 15 A3 D8 41 F4 04 5D C0 9C A3 B6 A6 A8 4A B5 B2 F9 3C E3 0B 93 5E E1 42 26 66 58 16 39 A4 9C 14 5D 69 E9 EE C8 7D 0F AC 85 E7 EC 9C 0B C4 E4 74 22
And finally the decrypted altered text:
D6 1E 4E A5 5A 8D 3B 4A E6 2F E2 0A 41 21 68 51 6E 8D 3B DA 74 58 62 F9 F9 D1 30 59 F5 FE 7D 54 14 79 42 14 B6 1D 34 C7 19 B0 68 67 36 25 D9 FA D0 1C 61 CB 40 A2 CD 77 6A 7D D3 D4 A2 23 9B 4F AF
