The message NOT NOW (numerically 131419131422) is to be sent to a user of the EIGamal system who has public key (37, 2, 18) and private key k = 17. If the integer j used to construct the ciphertext is changed over successive four-digit blocks from j = 13 to j = 28 to j = 11, what is the encrypted message produced? %3D %3D

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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**Problems 10.3**

1. The message "REPLY TODAY" is to be encrypted in the ElGamal cryptosystem and forwarded to a user with public key (47, 5, 10) and private key \( k = 19 \).

   (a) If the random integer chosen for encryption is \( j = 13 \), determine the ciphertext.
   
   (b) Indicate how the ciphertext can be decrypted using the recipient’s private key.

2. Suppose that the following ciphertext is received by a person with ElGamal public key (71, 7, 32) and private key \( k = 30 \):

   \[
   \begin{align*}
   (56, 45) & \quad (56, 38) & \quad (56, 29) & \quad (56, 03) \\
   (56, 67) & \quad (56, 05) & \quad (56, 27) & \quad (56, 31) \\
   (56, 38) & \quad (56, 29) & \\
   \end{align*}
   \]

   Obtain the plaintext message.

3. The message "NOT NOW" (numerically 131419131422) is to be sent to a user of the ElGamal system who has public key (37, 2, 18) and private key \( k = 17 \). If the integer \( j \) used to construct the ciphertext is changed over successive four-digit blocks from \( j = 13 \) to \( j = 28 \) to \( j = 11 \), what is the encrypted message produced?

4. Assume that a person has ElGamal public key (2633, 3, 1138) and private key \( k = 965 \). If the person selects the random integer \( j = 583 \) to encrypt the message "BEWARE OF THEM", obtain the resulting ciphertext.

   *Hint:* 
   \[
   3^{583} \equiv 1424 \, (\text{mod} \, 2633), \quad 1138^{583} \equiv 97 \, (\text{mod} \, 2633).
   \]

5. 

   (a) A person with public key (31, 2, 22)
Transcribed Image Text:**Problems 10.3** 1. The message "REPLY TODAY" is to be encrypted in the ElGamal cryptosystem and forwarded to a user with public key (47, 5, 10) and private key \( k = 19 \). (a) If the random integer chosen for encryption is \( j = 13 \), determine the ciphertext. (b) Indicate how the ciphertext can be decrypted using the recipient’s private key. 2. Suppose that the following ciphertext is received by a person with ElGamal public key (71, 7, 32) and private key \( k = 30 \): \[ \begin{align*} (56, 45) & \quad (56, 38) & \quad (56, 29) & \quad (56, 03) \\ (56, 67) & \quad (56, 05) & \quad (56, 27) & \quad (56, 31) \\ (56, 38) & \quad (56, 29) & \\ \end{align*} \] Obtain the plaintext message. 3. The message "NOT NOW" (numerically 131419131422) is to be sent to a user of the ElGamal system who has public key (37, 2, 18) and private key \( k = 17 \). If the integer \( j \) used to construct the ciphertext is changed over successive four-digit blocks from \( j = 13 \) to \( j = 28 \) to \( j = 11 \), what is the encrypted message produced? 4. Assume that a person has ElGamal public key (2633, 3, 1138) and private key \( k = 965 \). If the person selects the random integer \( j = 583 \) to encrypt the message "BEWARE OF THEM", obtain the resulting ciphertext. *Hint:* \[ 3^{583} \equiv 1424 \, (\text{mod} \, 2633), \quad 1138^{583} \equiv 97 \, (\text{mod} \, 2633). \] 5. (a) A person with public key (31, 2, 22)
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