Asymmetric encryption puzzle
Convert A = 1, B = 2, ..., Z = 26. Take the difference of (cipher text - key) modulo 26. Extend "EZRA" with itself. The third row is the difference between the first and second rows. There might be an error on 'B' and 'G'.

 M  E  D  M  T  B  J  B  M  A  E
13  5  4 13 20  2 10  2 13  1  5


 H  E  L  L  O  G  R  A  H  A  M
 8  5 12 12 15  7 18  1  8  1 13


 5 26 18  1  5 21 18  1  5 26 18


 E  Z  R  A  E  Z  R  A  E  Z  R
 5 26 18  1  5 26 18  1  5 26 18