The invention discloses a data encryption method and device, and a data decryption method and device. Wherein, the method includes: obtaining n+1 plaintext data m 0 , m 1 ,..., m n and n+1 key data k 0 , k 1 ,...,k n , wherein, the n+1 plaintext data is in one-to-one correspondence with the n+1 key data; with (k 0 , m 0 ), (k 1 , m 1 ),……, (k n , m n ) generate n degree polynomial F(x)=a for n+1 point coordinates 0 +a 1 *x+a 2 *x 2 +…+a n *x n , wherein, the n+1 points fall on the curve represented by the n-degree polynomial; the coefficient of the n-degree polynomial [a 0 , a 1 , a 2 …a n ] is determined as the ciphertext data corresponding to the n+1 plaintext data. The invention solves the technical problem of low transmission efficiency during encrypted data transmission during multi-party interaction.