Method for pseudonymizing, in particular, pseudonymizing character strings, wherein an original character string comprises a series of original characters, wherein, based on the method, the original character string is converted into an encrypted character string, which comprises a series of characters that have been altered with relation to the original character string, wherein each original character is an integral part of a defined character set, wherein a clear consecutive ordinal number is assigned to each character (11, 21), and wherein each original character is converted into an altered character, which is an integral part of the same defined character set of the original character, wherein, in a first alteration pass sequentially, in particular, all original characters of the original character string are changed into the altered characters, wherein the altered characters together form an encrypted character string, wherein, in a second alteration pass, in particular, all first altered characters are changed in an altered sequence into second altered characters, wherein the second altered characters together form a second encrypted character string, wherein each alteration pass comprises: specifying an alteration value, which is added to the ordinal number of the character to be altered, wherein: changing this character into the character of the character set in its alphabet whose ordinal number corresponds to the sum, then creating a new alteration value for the change of the next character to be altered, wherein the alteration value for each character is redefined on the basis of an output word generated by a cryptographic unit, wherein the cryptographic unit generates the output word depending on a previously altered character, in particular, the character immediately change beforehand, and wherein the cryptographic unit executes an AES algorithm to generate the output word. specifying an alteration value, which is added to the ordinal number of the character to be altered, wherein: changing this character into the character of the character set in its alphabet whose ordinal number corresponds to the sum, then creating a new alteration value for the change of the next character to be altered, wherein the alteration value for each character is redefined on the basis of an output word generated by a cryptographic unit, wherein the cryptographic unit generates the output word depending on a previously altered character, in particular, the character immediately change beforehand, and wherein the cryptographic unit executes an AES algorithm to generate the output word. changing this character into the character of the character set in its alphabet whose ordinal number corresponds to the sum, then creating a new alteration value for the change of the next character to be altered, wherein the alteration value for each character is redefined on the basis of an output word generated by a cryptographic unit, wherein the cryptographic unit generates the output word depending on a previously altered character, in particular, the character immediately change beforehand, and wherein the cryptographic unit executes an AES algorithm to generate the output word.