1# Certificate Extension Development 2 3 4This topic walks you through on how to create a certificate extension (**CertExtension**) instance, obtain the certificate extension information based on an object identifier (OID), and check whether the certificate is a CA certificate. 5 6 7## How to Develop 8 91. Import the [certFramework](../../reference/apis-device-certificate-kit/js-apis-cert.md) module. 10 ```ts 11 import certFramework from '@ohos.security.cert'; 12 ``` 13 142. Use [cryptoCert.createCertExtension](../../reference/apis-device-certificate-kit/js-apis-cert.md#cryptocertcreatecertextension10) to create a **CertExtension** instance. 15 163. Use [CertExtension.getEntry](../../reference/apis-device-certificate-kit/js-apis-cert.md#getentry10) to obtain the certificate extension of the specified OID. 17 18 194. Use [CertExtension.checkCA](../../reference/apis-device-certificate-kit/js-apis-cert.md#checkca10) to check whether the certificate is a CA certificate. 20 21```ts 22import certFramework from '@ohos.security.cert'; 23import { BusinessError } from '@ohos.base'; 24import util from '@ohos.util'; 25 26// Certificate extension data. The following is only an example. 27let extData = new Uint8Array([ 28 0x30, 0x40, 0x30, 0x0F, 0x06, 0x03, 0x55, 0x1D, 29 0x13, 0x01, 0x01, 0xFF, 0x04, 0x05, 0x30, 0x03, 30 0x01, 0x01, 0xFF, 0x30, 0x0E, 0x06, 0x03, 0x55, 31 0x1D, 0x0F, 0x01, 0x01, 0xFF, 0x04, 0x04, 0x03, 32 0x02, 0x01, 0xC6, 0x30, 0x1D, 0x06, 0x03, 0x55, 33 0x1D, 0x0E, 0x04, 0x16, 0x04, 0x14, 0xE0, 0x8C, 34 0x9B, 0xDB, 0x25, 0x49, 0xB3, 0xF1, 0x7C, 0x86, 35 0xD6, 0xB2, 0x42, 0x87, 0x0B, 0xD0, 0x6B, 0xA0, 36 0xD9, 0xE4 37]); 38 39// Certificate extension example. 40function certExtensionSample(): void { 41 let textEncoder = new util.TextEncoder(); 42 let encodingBlob: certFramework.EncodingBlob = { 43 data: extData, 44 // Certificate extension format. Currently, only the DER format is supported. 45 encodingFormat: certFramework.EncodingFormat.FORMAT_DER 46 }; 47 48 // Create a CertExtension instance. 49 certFramework.createCertExtension(encodingBlob, (err, certExtension) => { 50 if (err != null) { 51 // The CertExtension instance fails to be created. 52 console.error(`createCertExtension failed, errCode:${err.code}, errMsg:${err.message} `); 53 return; 54 } 55 // The CertExtension instance is created. 56 console.log('createCertExtension success'); 57 58 try { 59 // Obtain the certificate extension information based on an OID. 60 let oidData = '2.5.29.14'; 61 let oid: certFramework.DataBlob = { 62 data: textEncoder.encodeInto(oidData), 63 } 64 let entry = certExtension.getEntry(certFramework.ExtensionEntryType.EXTENSION_ENTRY_TYPE_ENTRY, oid); 65 66 // Check whether the certificate is a CA certificate. 67 let pathLen = certExtension.checkCA(); 68 console.log('test cert extension success'); 69 } catch (err) { 70 let e: BusinessError = err as BusinessError; 71 console.error(`operation failed, message:${e.message} ,code:${e.code} `); 72 } 73 }); 74} 75``` 76