Here’s a simple example on how to request a trusted timestamping service from a certificate authority using TSP (Time-Stamp Protocol). It’s really simple if the server allows you to use standard HTTP interface instead of full TSP interface. The code is below. What it does is hashes an example string and requests its trusted timestamp from time.certum.pl, courtesy of Unizeto certification authority.
The output file is binary, DER encoded PKCS#7 structure containing timestamp signed by the TSP service. It can be parsed with anything that understands PKCS#7:
$ openssl asn1parse -i -inform DER -in response.tsp
0:d=0 hl=4 l=1804 cons: SEQUENCE
4:d=1 hl=2 l= 9 prim: OBJECT :pkcs7-signedData
15:d=1 hl=4 l=1789 cons: cont [ 0 ]
19:d=2 hl=4 l=1785 cons: SEQUENCE
23:d=3 hl=2 l= 1 prim: INTEGER :03
26:d=3 hl=2 l= 9 cons: SET
28:d=4 hl=2 l= 7 cons: SEQUENCE
30:d=5 hl=2 l= 5 prim: OBJECT :sha1
37:d=3 hl=3 l= 238 cons: SEQUENCE
40:d=4 hl=2 l= 11 prim: OBJECT :id-smime-ct-TSTInfo
53:d=4 hl=3 l= 222 cons: cont [ 0 ]
56:d=5 hl=3 l= 219 prim: OCTET STRING
278:d=3 hl=4 l= 940 cons: cont [ 0 ]
282:d=4 hl=4 l= 936 cons: SEQUENCE
286:d=5 hl=4 l= 656 cons: SEQUENCE
290:d=6 hl=2 l= 3 cons: cont [ 0 ]
292:d=7 hl=2 l= 1 prim: INTEGER :02
295:d=6 hl=2 l= 3 prim: INTEGER :047A55
300:d=6 hl=2 l= 13 cons: SEQUENCE
302:d=7 hl=2 l= 9 prim: OBJECT :sha1WithRSAEncryption
313:d=7 hl=2 l= 0 prim: NULL
315:d=6 hl=2 l= 62 cons: SEQUENCE
317:d=7 hl=2 l= 11 cons: SET
319:d=8 hl=2 l= 9 cons: SEQUENCE
321:d=9 hl=2 l= 3 prim: OBJECT :countryName
326:d=9 hl=2 l= 2 prim: PRINTABLESTRING :PL
330:d=7 hl=2 l= 27 cons: SET
332:d=8 hl=2 l= 25 cons: SEQUENCE
334:d=9 hl=2 l= 3 prim: OBJECT :organizationName
339:d=9 hl=2 l= 18 prim: PRINTABLESTRING :Unizeto Sp. z o.o.
359:d=7 hl=2 l= 18 cons: SET
361:d=8 hl=2 l= 16 cons: SEQUENCE
363:d=9 hl=2 l= 3 prim: OBJECT :commonName
368:d=9 hl=2 l= 9 prim: PRINTABLESTRING :Certum CA
379:d=6 hl=2 l= 30 cons: SEQUENCE
381:d=7 hl=2 l= 13 prim: UTCTIME :090303125815Z
396:d=7 hl=2 l= 13 prim: UTCTIME :240303125815Z
411:d=6 hl=3 l= 131 cons: SEQUENCE
414:d=7 hl=2 l= 11 cons: SET
416:d=8 hl=2 l= 9 cons: SEQUENCE
418:d=9 hl=2 l= 3 prim: OBJECT :countryName
423:d=9 hl=2 l= 2 prim: PRINTABLESTRING :PL
427:d=7 hl=2 l= 34 cons: SET
429:d=8 hl=2 l= 32 cons: SEQUENCE
431:d=9 hl=2 l= 3 prim: OBJECT :organizationName
436:d=9 hl=2 l= 25 prim: PRINTABLESTRING :Unizeto Technologies S.A.
463:d=7 hl=2 l= 39 cons: SET
465:d=8 hl=2 l= 37 cons: SEQUENCE
467:d=9 hl=2 l= 3 prim: OBJECT :organizationalUnitName
472:d=9 hl=2 l= 30 prim: PRINTABLESTRING :Certum Certification Authority
504:d=7 hl=2 l= 39 cons: SET
506:d=8 hl=2 l= 37 cons: SEQUENCE
508:d=9 hl=2 l= 3 prim: OBJECT :commonName
513:d=9 hl=2 l= 30 prim: PRINTABLESTRING :Certum Time-Stamping Authority
545:d=6 hl=4 l= 290 cons: SEQUENCE
549:d=7 hl=2 l= 13 cons: SEQUENCE
551:d=8 hl=2 l= 9 prim: OBJECT :rsaEncryption
562:d=8 hl=2 l= 0 prim: NULL
564:d=7 hl=4 l= 271 prim: BIT STRING
839:d=6 hl=2 l= 105 cons: cont [ 3 ]
841:d=7 hl=2 l= 103 cons: SEQUENCE
843:d=8 hl=2 l= 22 cons: SEQUENCE
845:d=9 hl=2 l= 3 prim: OBJECT :X509v3 Extended Key Usage
850:d=9 hl=2 l= 1 prim: BOOLEAN :255
853:d=9 hl=2 l= 12 prim: OCTET STRING
867:d=8 hl=2 l= 44 cons: SEQUENCE
869:d=9 hl=2 l= 3 prim: OBJECT :X509v3 CRL Distribution Points
874:d=9 hl=2 l= 37 prim: OCTET STRING
913:d=8 hl=2 l= 31 cons: SEQUENCE
915:d=9 hl=2 l= 3 prim: OBJECT :X509v3 Subject Alternative Name
920:d=9 hl=2 l= 24 prim: OCTET STRING
946:d=5 hl=2 l= 13 cons: SEQUENCE
948:d=6 hl=2 l= 9 prim: OBJECT :sha1WithRSAEncryption
959:d=6 hl=2 l= 0 prim: NULL
961:d=5 hl=4 l= 257 prim: BIT STRING
1222:d=3 hl=4 l= 582 cons: SET
1226:d=4 hl=4 l= 578 cons: SEQUENCE
1230:d=5 hl=2 l= 1 prim: INTEGER :01
1233:d=5 hl=2 l= 69 cons: SEQUENCE
1235:d=6 hl=2 l= 62 cons: SEQUENCE
1237:d=7 hl=2 l= 11 cons: SET
1239:d=8 hl=2 l= 9 cons: SEQUENCE
1241:d=9 hl=2 l= 3 prim: OBJECT :countryName
1246:d=9 hl=2 l= 2 prim: PRINTABLESTRING :PL
1250:d=7 hl=2 l= 27 cons: SET
1252:d=8 hl=2 l= 25 cons: SEQUENCE
1254:d=9 hl=2 l= 3 prim: OBJECT :organizationName
1259:d=9 hl=2 l= 18 prim: PRINTABLESTRING :Unizeto Sp. z o.o.
1279:d=7 hl=2 l= 18 cons: SET
1281:d=8 hl=2 l= 16 cons: SEQUENCE
1283:d=9 hl=2 l= 3 prim: OBJECT :commonName
1288:d=9 hl=2 l= 9 prim: PRINTABLESTRING :Certum CA
1299:d=6 hl=2 l= 3 prim: INTEGER :047A55
1304:d=5 hl=2 l= 9 cons: SEQUENCE
1306:d=6 hl=2 l= 5 prim: OBJECT :sha1
1313:d=6 hl=2 l= 0 prim: NULL
1315:d=5 hl=3 l= 215 cons: cont [ 0 ]
1318:d=6 hl=2 l= 26 cons: SEQUENCE
1320:d=7 hl=2 l= 9 prim: OBJECT :contentType
1331:d=7 hl=2 l= 13 cons: SET
1333:d=8 hl=2 l= 11 prim: OBJECT :id-smime-ct-TSTInfo
1346:d=6 hl=2 l= 28 cons: SEQUENCE
1348:d=7 hl=2 l= 9 prim: OBJECT :signingTime
1359:d=7 hl=2 l= 15 cons: SET
1361:d=8 hl=2 l= 13 prim: UTCTIME :120318141833Z
1376:d=6 hl=2 l= 35 cons: SEQUENCE
1378:d=7 hl=2 l= 9 prim: OBJECT :messageDigest
1389:d=7 hl=2 l= 22 cons: SET
1391:d=8 hl=2 l= 20 prim: OCTET STRING
1413:d=6 hl=2 l= 118 cons: SEQUENCE
1415:d=7 hl=2 l= 11 prim: OBJECT :id-smime-aa-signingCertificate
1428:d=7 hl=2 l= 103 cons: SET
1430:d=8 hl=2 l= 101 cons: SEQUENCE
1432:d=9 hl=2 l= 99 cons: SEQUENCE
1434:d=10 hl=2 l= 97 cons: SEQUENCE
1436:d=11 hl=2 l= 20 prim: OCTET STRING
1458:d=11 hl=2 l= 73 cons: SEQUENCE
1460:d=12 hl=2 l= 66 cons: SEQUENCE
1462:d=13 hl=2 l= 64 cons: cont [ 4 ]
1464:d=14 hl=2 l= 62 cons: SEQUENCE
1466:d=15 hl=2 l= 11 cons: SET
1468:d=16 hl=2 l= 9 cons: SEQUENCE
1470:d=17 hl=2 l= 3 prim: OBJECT :countryName
1475:d=17 hl=2 l= 2 prim: PRINTABLESTRING :PL
1479:d=15 hl=2 l= 27 cons: SET
1481:d=16 hl=2 l= 25 cons: SEQUENCE
1483:d=17 hl=2 l= 3 prim: OBJECT :organizationName
1488:d=17 hl=2 l= 18 prim: PRINTABLESTRING :Unizeto Sp. z o.o.
1508:d=15 hl=2 l= 18 cons: SET
1510:d=16 hl=2 l= 16 cons: SEQUENCE
1512:d=17 hl=2 l= 3 prim: OBJECT :commonName
1517:d=17 hl=2 l= 9 prim: PRINTABLESTRING :Certum CA
1528:d=12 hl=2 l= 3 prim: INTEGER :047A55
1533:d=5 hl=2 l= 13 cons: SEQUENCE
1535:d=6 hl=2 l= 9 prim: OBJECT :rsaEncryption
1546:d=6 hl=2 l= 0 prim: NULL
1548:d=5 hl=4 l= 256 prim: OCTET STRING