(Objective-C) RSASSA-PSS Sign Text

Signs text to create a PKCS7/CMS signature. The signature algorithm is RSASSA-PSS with SHA256.

Note: This example requires Chilkat v9.5.0.67 or greater.

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#import <CkoCrypt2.h>
#import <CkoPfx.h>
#import <CkoCert.h>
#import <CkoStringBuilder.h>
#import <NSString.h>

// This example requires the Chilkat Crypt API to have been previously unlocked.
// See Unlock Chilkat Crypt for sample code.

CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];

// Get a digital certificate with private key from a .pfx
// (Chilkat has many different ways to provide a cert + private key for siging.
// Using a PFX is just one possible option.)
CkoPfx *pfx = [[CkoPfx alloc] init];
BOOL success = [pfx LoadPfxFile: @"qa_data/rsassa-pss/privatekey.pfx" password: @"PFX_PASSWORD"];
if (success != YES) {
    NSLog(@"%@",pfx.LastErrorText);
    return;
}

// Get the certificate to be used for signing.
// (The typical case for a PFX is that it contains a cert with an associated private key,
// as well as other certificates in the chain of authentication.  The cert with the private
// key should be in the first position at index 0.)
CkoCert *cert = [pfx GetCert: [NSNumber numberWithInt: 0]];
if (pfx.LastMethodSuccess != YES) {
    NSLog(@"%@",pfx.LastErrorText);
    return;
}

[crypt SetSigningCert: cert];

// Indicate that RSASSA-PSS with SHA256 should be used.
crypt.SigningAlg = @"pss";
crypt.HashAlgorithm = @"sha256";

crypt.EncodingMode = @"base64_mime";

// Build a string to sign
CkoStringBuilder *sb = [[CkoStringBuilder alloc] init];
int i = 1;
while (i < 12) {
    [sb AppendInt: [NSNumber numberWithInt: i]];
    [sb Append: @" the quick brown fox jumped over the lazy dog.\r\n"];
    i = i + 1;
}

NSLog(@"%@",[sb GetAsString]);

// The string to be encrypted looks like this:

// 1 the quick brown fox jumped over the lazy dog.
// 2 the quick brown fox jumped over the lazy dog.
// 3 the quick brown fox jumped over the lazy dog.
// 4 the quick brown fox jumped over the lazy dog.
// ...

// Make sure to specify the byte representation (character encoding)
crypt.Charset = @"utf-8";

// Sign the string to get a PKCS7 detached signature in base64 format.
NSString *pkcs7sig = [crypt SignSbENC: sb];
NSLog(@"%@",@"Detached PCKS7 Signature:");
NSLog(@"%@",pkcs7sig);

// This signature looks like this:

// MIIG5wYJKoZIhvcNAQcCoIIG2DCCBtQCAQExDzANBglghkgBZQMEAgEFADALBgkqhkiG9w0BBwGg
// ggL4MIIC9DCCAl2gAwIBAgIJAMPsJCT11cniMA0GCSqGSIb3DQEBCwUAMIGSMQswCQYDVQQGEwJB
// VTERMA8GA1UECAwIVmljdG9yaWExEjAQBgNVBAcMCU1lbGJvdXJuZTEhMB8GA1UECgwYSW50ZXJu
// ZXQgV2lkZ2l0cyBQdHkgTHRkMQ8wDQYDVQQDDAZXaWRnZXQxKDAmBgkqhkiG9w0BCQEWGWFkbWlu
// QGludGVybmV0d2lkZ2V0cy5jb20wHhcNMTYxMTAxMTY1MjMyWhcNMjExMDMxMTY1MjMyWjCBkjEL
// MAkGA1UEBhMCQVUxETAPBgNVBAgMCFZpY3RvcmlhMRIwEAYDVQQHDAlNZWxib3VybmUxITAfBgNV
// BAoMGEludGVybmV0IFdpZGdpdHMgUHR5IEx0ZDEPMA0GA1UEAwwGV2lkZ2V0MSgwJgYJKoZIhvcN
// AQkBFhlhZG1pbkBpbnRlcm5ldHdpZGdldHMuY29tMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKB
// gQDGIdoCjyavs+F/Rm0VIB4m6O7VL1j+1IqieoR9NEX2GQvu2VCdceyxf9qaw1bxipEvjLwUkw7M
// e+BTlLpWQbBMH87s6KpsC8MVyXhMLpP0oM8NFix/vLz2wdLhUh7CZvJA0plqkJk9bj57QIu+EO1k
// tUHM2DFb6sckvCL2yybD1wIDAQABo1AwTjAdBgNVHQ4EFgQUONKKu2zsXIrinWxIGT654vrcQwsw
// HwYDVR0jBBgwFoAUONKKu2zsXIrinWxIGT654vrcQwswDAYDVR0TBAUwAwEB/zANBgkqhkiG9w0B
// AQsFAAOBgQArFvdi5u9i2QF1Qw+cdC1l7w2Y3+q6RIkln2W8rWJFje00644o8hXy7v46giJCedmF
// ULlhm1n7XIsZGy2W3lJ77v5agn9gFwXu1h3cqkGXkoteE6SQJQXWgsW3GWPveObvTL8LF4y57fgM
// 9ZWS+V9MJajeu44Rf/tU17TLYKjvEjGCA7MwggOvAgEBMIGgMIGSMQswCQYDVQQGEwJBVTERMA8G
// A1UECAwIVmljdG9yaWExEjAQBgNVBAcMCU1lbGJvdXJuZTEhMB8GA1UECgwYSW50ZXJuZXQgV2lk
// Z2l0cyBQdHkgTHRkMQ8wDQYDVQQDDAZXaWRnZXQxKDAmBgkqhkiG9w0BCQEWGWFkbWluQGludGVy
// bmV0d2lkZ2V0cy5jb20CCQDD7CQk9dXJ4jANBglghkgBZQMEAgEFAKCCAjQwGAYJKoZIhvcNAQkD
// MQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTcwNDI5MTYzNTQ3WjAvBgkqhkiG9w0BCQQx
// IgQgnXqtpfBjs9ZZUJxbNYbwYvpmXTGgIbYErkIA3jQo0EEwXwYJKoZIhvcNAQkPMVIwUDALBglg
// hkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3DQMCAgFAMAcGBSsO
// AwIHMA0GCCqGSIb3DQMCAgEoMIGxBgkrBgEEAYI3EAQxgaMwgaAwgZIxCzAJBgNVBAYTAkFVMREw
// DwYDVQQIDAhWaWN0b3JpYTESMBAGA1UEBwwJTWVsYm91cm5lMSEwHwYDVQQKDBhJbnRlcm5ldCBX
// aWRnaXRzIFB0eSBMdGQxDzANBgNVBAMMBldpZGdldDEoMCYGCSqGSIb3DQEJARYZYWRtaW5AaW50
// ZXJuZXR3aWRnZXRzLmNvbQIJAMPsJCT11cniMIGzBgsqhkiG9w0BCRACCzGBo6CBoDCBkjELMAkG
// A1UEBhMCQVUxETAPBgNVBAgMCFZpY3RvcmlhMRIwEAYDVQQHDAlNZWxib3VybmUxITAfBgNVBAoM
// GEludGVybmV0IFdpZGdpdHMgUHR5IEx0ZDEPMA0GA1UEAwwGV2lkZ2V0MSgwJgYJKoZIhvcNAQkB
// FhlhZG1pbkBpbnRlcm5ldHdpZGdldHMuY29tAgkAw+wkJPXVyeIwPQYJKoZIhvcNAQEKMDCgDTAL
// BglghkgBZQMEAgGhGjAYBgkqhkiG9w0BAQgwCwYJYIZIAWUDBAIBogMCASAEgYBFgBS1vtBoac6P
// /NRcY3jdytoxK7xc8vEYW/PhgsbE+sP7dvu6eoRLVicoQ8RIeMh3CtPZFq1+JcL5NNzQoAotizTX
// EKhiceX1mC5ocCeEvgNouxkN2Qr/X12m60rNvNl5r+GEqiqx/1fs2yRAl5sIzwPsMMY3p9tGOpy0
// 5p7sRQ==

// The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
// then copy-and-paste the Base64 signature into the form and decode..

// The signature can be verified against the original data like this:
success = [crypt VerifySbENC: sb encodedSig: pkcs7sig];
NSLog(@"%@%d",@"Signature verified: ",success);