(4) Elgamal public key cryptosystem (encryption): Start with the prime p = 29 and the primitive root g = 2. Alice sends Bob the public key A = 3. Bob wants to send the message m₁ = 15 to Alice. Bob chooses the random element k = 5. Using the Elgamal public key cryptosystem, compute the pair of numbers (C₁, C₂) that Bob sends to Alice.

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Chapter2: Second-order Linear Odes
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### Elgamal Public Key Cryptosystem (Encryption):

Consider the following example to understand the Elgamal public key cryptosystem for encryption:

1. **Initialization**:
   - Start with the prime \( p = 29 \) and the primitive root \( g = 2 \).

2. **Public Key Exchange**:
   - Alice sends Bob the public key \( A = 3 \).

3. **Message Preparation**:
   - Bob wants to send the message \( m_1 = 15 \) to Alice.

4. **Random Element Selection**:
   - Bob chooses the random element \( k = 5 \).

5. **Encryption**:
   - Using the Elgamal public key cryptosystem, compute the pair of numbers \( (c_1, c_2) \) that Bob sends to Alice.

#### Computation:

To compute the pair \( (c_1, c_2) \):
1. Calculate \( c_1 \):
   \[
   c_1 = g^k \mod p
   \]
   Substituting the values:
   \[
   c_1 = 2^5 \mod 29
   \]
   \[
   c_1 = 32 \mod 29
   \]
   \[
   c_1 = 3
   \]

2. Calculate \( c_2 \):
   \[
   c_2 = m_1 \cdot A^k \mod p
   \]
   Substituting the values:
   \[
   c_2 = 15 \cdot 3^5 \mod 29
   \]
   \[
   3^5 = 243
   \]
   \[
   243 \mod 29 = 11
   \]
   \[
   c_2 = 15 \cdot 11 \mod 29
   \]
   \[
   c_2 = 165 \mod 29
   \]
   \[
   c_2 = 20
   \]

So, the pair of numbers \( (c_1, c_2) \) that Bob sends to Alice are:
\[
(c_1, c_2) = (3, 20)
\]

### Summary:
- Prime \( p \): \( 29 \)
- Primitive Root \( g \): \( 2
Transcribed Image Text:### Elgamal Public Key Cryptosystem (Encryption): Consider the following example to understand the Elgamal public key cryptosystem for encryption: 1. **Initialization**: - Start with the prime \( p = 29 \) and the primitive root \( g = 2 \). 2. **Public Key Exchange**: - Alice sends Bob the public key \( A = 3 \). 3. **Message Preparation**: - Bob wants to send the message \( m_1 = 15 \) to Alice. 4. **Random Element Selection**: - Bob chooses the random element \( k = 5 \). 5. **Encryption**: - Using the Elgamal public key cryptosystem, compute the pair of numbers \( (c_1, c_2) \) that Bob sends to Alice. #### Computation: To compute the pair \( (c_1, c_2) \): 1. Calculate \( c_1 \): \[ c_1 = g^k \mod p \] Substituting the values: \[ c_1 = 2^5 \mod 29 \] \[ c_1 = 32 \mod 29 \] \[ c_1 = 3 \] 2. Calculate \( c_2 \): \[ c_2 = m_1 \cdot A^k \mod p \] Substituting the values: \[ c_2 = 15 \cdot 3^5 \mod 29 \] \[ 3^5 = 243 \] \[ 243 \mod 29 = 11 \] \[ c_2 = 15 \cdot 11 \mod 29 \] \[ c_2 = 165 \mod 29 \] \[ c_2 = 20 \] So, the pair of numbers \( (c_1, c_2) \) that Bob sends to Alice are: \[ (c_1, c_2) = (3, 20) \] ### Summary: - Prime \( p \): \( 29 \) - Primitive Root \( g \): \( 2
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