2011/11/8 Carlos Rabassa <<a href="mailto:carnen@mac.com">carnen@mac.com</a>> <div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"> <div style="word-wrap: break-word;"><div><div><div>English Text:</div></div><div> </div> <div><div>We believe this could be an interesting subject for a project using some of the applications in the Plan Ceibal computers. </div></div></div></div><div style="word-wrap: break-word;"> <div><div><div><div> </div></div></div></div></div></blockquote><div> </div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word;"> <div><div><div><div><div style="font-size: medium;">The first project we would like to suggest is to just repeat the calculation we show, using one or more of the applications in Plan Ceibal´ computers.</div> <div style="font-size: medium;"> </div><div style="font-size: medium;">Then, it could be resolving other problems:</div><div style="font-size: medium;"> </div><div style="font-size: medium;"> - Given seven of the eight digits in an ID card, calculate the missing digit.</div> <div style="font-size: medium;"> </div> <div style="font-size: medium;">- Whenever there is an error, is the calculation going to return the wrong control digit? Justify the answer.</div> <div style="font-size: medium;"> </div><div style="font-size: medium;">- If we transpose two consecutive digits, a very frequent error, will the calculation result change? Are we going to be able, in such case, to find out what the error was and correct it?</div> <div style="font-size: medium;"> </div><div style="font-size: medium;">- Are there other applications in the real world for control digits, besides the ID card?</div> </div></div></div><div style="font-size: medium;"> </div><div style="font-size: medium;">We will be glad to send the paper by Omar Gil and Ricardo Vilaró, mentioned in the attached spreadsheet, to anyone who might wish to further study the subject and do other exercises.</div> </div></div></blockquote></div> [Español abajo] Carlos, The system you describe is generally referred to as a "checksum". <a href="http://en.wikipedia.org/wiki/Checksum">http://en.wikipedia.org/wiki/Checksum</a> <a href="http://es.wikipedia.org/wiki/Suma_de_verificaci%C3%B3n">http://es.wikipedia.org/wiki/Suma_de_verificaci%C3%B3n</a> There are multiple algorithms for calculating check sums and each has fdifferent features. Checksum methods typically employ some form of hashing (from the simple to the complex) and depending on the hashing algorithm used and the construction of the identifier they are used on (e.g. all digits, digits and letters) , checksums are capable of detecting transposition errors, simple single substitutions and / or double substitutions. <a href="http://en.wikipedia.org/wiki/List_of_hash_functions">http://en.wikipedia.org/wiki/List_of_hash_functions</a> Checksums are widely used in barcoding applications and data transmission to look for data corruption. They are used in all banking transactions and are probably printed on your checkbook. The International Standards Organization publishes: ISO/IEC 7064:2003 "Information technology -- Security techniques -- Check character systems" whcih contains a description of a great many checksum systems and their applicability to different identifier structures. An understanding of checksums and their characteristics would certainly be a lesson worth learning for anyone interested in how their information is passed within computer systems. it is also an introduction of computing concepts like error correction. cjl [Español] El sistema usted describe es generalmente denomina "checksum". <a href="http://en.wikipedia.org/wiki/Checksum">http://en.wikipedia.org/wiki/Checksum</a> <a href="http://es.wikipedia.org/wiki/Suma_de_verificaci%C3%B3n">http://es.wikipedia.org/wiki/Suma_de_verificaci%C3%B3n</a> Hay algoritmos múltiples para sumas comprobar calcular y cada tiene características distintas. Métodos Checksum emplean típicamente alguna forma de hashing (del simple a lo complejo) y dependiendo del algoritmo hashing utilizado y la confección del identificador se utilizan en (p.ej. todos dígitos, dígitos y letras), checksums son capaces de detectar errores transposición , simple sustituciones sola y / o sustituciones doble. <a href="http://en.wikipedia.org/wiki/List_of_hash_functions">http://en.wikipedia.org/wiki/List_of_hash_functions</a> Checksums se ampliamente utilizado en códigos de barras aplicaciones y transmisión datos para buscar corrupción datos. Se utilizan en todas transacciones bancarias y son probablemente impreso en su chequera. La Organización Normas Internacionales publica: ISO / IEC 7064:2003 "tecnología información - Técnicas Seguridad - Compruebe sistemas carácter" que contiene una descripción de un sistemas checksum gran muchos y su aplicabilidad a estructuras identificador diferente. Una comprensión de checksums y sus características ciertamente sería una lección pena aprender para cualquiera interesado en cómo sus información se pasa dentro sistemas informáticos. también es una introducción de conceptos computación como corrección error.