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Alice and Bob agreed to use an ECBC-MAC scheme (i.e. using a block cipher in CBC mode to construct a MAC scheme) with only one key k that they already agreed upon and share. The ECBC-MAC scheme in question is existentially unforgeable with respect to fixed-length messages. Alice and Bob agreed to extend the MAC scheme to support arbitrary- length messages. Alice has initialized a local counter A to zero on her end and similarly Bob initialized a local variable B to zero on his end. When Alice would like to sign a message M, Alice increments her local variable A and sends (M, T-ECBC- MACK(A||M)) to Bob. To verify a received MAC tag T, Bob increments his own local variable B and only accepts if the received MAC tag T is equal to ECBC-MAC (B||M), where || denotes concatenation. Does this modified MAC scheme preserve existential unforgeability with respect to arbitrary-length messages? Yes No

Alice and Bob agreed to use an ECBC-MAC scheme (i.e. using a block cipher in CBC mode to construct a MAC scheme) with only one key k that they already agreed upon and share. The ECBC-MAC scheme in question is existentially unforgeable with respect to fixed-length messages. Alice and Bob agreed to extend the MAC scheme to support arbitrary- length messages. Alice has initialized a local counter A to zero on her end and similarly Bob initialized a local variable B to zero on his end. When Alice would like to sign a message M, Alice increments her local variable A and sends (M, T-ECBC- MACK(A||M)) to Bob. To verify a received MAC tag T, Bob increments his own local variable B and only accepts if the received MAC tag T is equal to ECBC-MAC (B||M), where || denotes concatenation. Does this modified MAC scheme preserve existential unforgeability with respect to arbitrary-length messages? Yes No

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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Alice and Bob agreed to use an ECBC-MAC scheme (i.e. using a block cipher in CBC mode to construct a MAC scheme) with only one key k that they already agreed upon and share. The ECBC-MAC scheme in question is existentially unforgeable with respect to fixed-length messages. Alice and Bob agreed to extend the MAC scheme to support arbitrary- length messages. Alice has initialized a local counter A to zero on her end and similarly Bob initialized a local variable B to zero on his end. When Alice would like to sign a message M, Alice increments her local variable A and sends (M, T=ECBC- MACK(A||M)) to Bob. To verify a received MAC tag T, Bob increments his own local variable B and only accepts if the received MAC tag T is equal to ECBC-MACK(B||M), where || denotes concatenation. Does this modified MAC scheme preserve existential unforgeability with respect to arbitrary-length messages? Yes No
Transcribed Image Text:Alice and Bob agreed to use an ECBC-MAC scheme (i.e. using a block cipher in CBC mode to construct a MAC scheme) with only one key k that they already agreed upon and share. The ECBC-MAC scheme in question is existentially unforgeable with respect to fixed-length messages. Alice and Bob agreed to extend the MAC scheme to support arbitrary- length messages. Alice has initialized a local counter A to zero on her end and similarly Bob initialized a local variable B to zero on his end. When Alice would like to sign a message M, Alice increments her local variable A and sends (M, T=ECBC- MACK(A||M)) to Bob. To verify a received MAC tag T, Bob increments his own local variable B and only accepts if the received MAC tag T is equal to ECBC-MACK(B||M), where || denotes concatenation. Does this modified MAC scheme preserve existential unforgeability with respect to arbitrary-length messages? Yes No
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