The method described by you had been in use since the 19th century (typically using a designated book as the one-time pad), but it was cracked at the end of WWI

The method described by you had been in use since the 19th century (typically using a designated book as the one-time pad), but it was cracked at the end of WWI, in 1918, by an American cryptographer, William Frederick Friedman, who was thus the first who has demonstrated that it is not enough for the encryption mask stream to be non-periodic, but it must also be random, otherwise it is still possible to decrypt the message by statistical analysis. This fact proved by Friedman in 1918 has become widely known a few years later, in 1926, when Gilbert Sandford Vernam has published an article "Cipher Printing Telegraph Systems For Secret Wire and Radio Telegraphic Communications" in a journal. While Vernam mentioned the help from Friedman, he gave no details and the works written by Friedman for the education of American cryptographers have remained classified for many decades. Because of this, secure one-time pads have been referred frequently as the Vernam cipher, but this is wrong, as he is not its inventor, but only the first who has mentioned it in the non-classified literature. Vernam (as a Bell Labs engineer) had a very important contribution to cryptography, but of a different kind. He has invented enciphering by modulo-2 sum (a.k.a. XOR), which is cheaper to implement in hardware than the integer addition used previously.