Vigenère Cipher

Black Widow and Hawkeye need to plan a surprise birthday party for Nick Fury, and they decide to encrypt their messages so Nick can't read them. They use the Vigenère cipher, a simple form of polyalphabetic substitution first described by Giovan Battista Bellaso in 1553.

The Vigenère cipher generalizes the Caesar cipher. In a Caesar cipher, every letter is shifted by the same fixed amount; for example, with a shift of 3, A becomes D, B becomes E, and Y becomes B (wrapping around the end of the alphabet). The Vigenère cipher instead applies a sequence of Caesar ciphers with different shift amounts.

To encrypt, the sender picks a keyword and repeats it until it is as long as the plaintext. For plaintext ATTACKATDAWN and keyword LEMON, the repeated key is:

Plaintext: ATTACKATDAWN
Keyword:   LEMONLEMONLE

Each plaintext letter is shifted by the amount given by the aligned keyword letter, where a letter's shift is its position in the alphabet (A = 0, B = 1, …, Z = 25). So a keyword letter L shifts by 11: A becomes L, B becomes M, and after Z the alphabet wraps back to A. A keyword letter E shifts by 4, so T becomes X.

Formally, let the plaintext letters be $P_0 P_1 \dots$ and the repeated keyword letters be $K_0 K_1 \dots$; then each ciphertext letter is $C_i = (P_i + K_i) \bmod 26$, using the alphabet positions above.

Following this rule, ATTACKATDAWN under keyword LEMON encrypts to LXFOPVEFRNHR.

Write a program that encrypts messages with the Vigenère cipher.

The first line contains the number of test cases $T$ ($T < 100$).

Each of the next $T$ lines contains one test case: a keyword and a plaintext, separated by a single space. Both strings consist only of uppercase letters A–Z (any digits, punctuation, and whitespace have already been stripped out).

For each test case, print one line in the form:

Ciphertext: <encrypted text>

where <encrypted text> is the plaintext encrypted with the given keyword using the Vigenère cipher.