A lot of the answers already provided are overlooking the interception capability of the ISP or NSA. Take a look at Room 641A in the AT&T datacenter. There are an estimated 10 to 20 such facilities that have been installed throughout the United States. Also take a look at the One Wilshire building where 260 ISP's connections converge into one building. That location is a prime location for an interception facility.

The fact is an ISP (or the equipment installed by the NSA in the ISP) can intercept and MITM attack an SSL connection and they can do it quite easily actually.

• Your web browser or operating system has over 500 trusted certificates installed in it. This means that you implicitly trust any website whose certificate has been signed by this certificate.
• The NSA via secret FISA court order can force any Certificate Authority operating in the United States to give them their root certificate. The court order includes a special non disclosure clause which forces the CA to keep their mouth shut under penalty of jail time if they speak out about it. They may not even need to do this however, they only need to convince the browser vendors to accept one NSA owned certificate as trusted in the browser.
• As your traffic passes through the ISP they swap out the website's true public key with the NSA's own public key signed by the compromised certificate authority thus performing the MITM attack.
• Your web browser accepts this false certificate as trusted and you communicate the symmetric encryption key for the exchange back to the NSA/ISP who keep a copy of it and also pass the same key onto the website.
• Your session with the website is decrypted in real-time with the compromised symmetric key.
• The decrypted data is sent via fibre optic line to the NSA's headquarters and data center in the basement of Fort Meade. This scans the data for hundreds or thousands of keywords that may indicate various types of threats. Any keywords are red-flagged for an analyst to view and prioritize further action if any. The final data is sent to one of the NSA's data storage facilities in the US. The new storage facility is the Utah datacenter which is likely online already as it was scheduled to be online at the end of last month.

Here's a diagram from nsawatch.org:

A lot of the answers already provided are overlooking the interception capability of the ISP or NSA. Take a look at Room 641A in the AT&T datacenter. There are an estimated 10 to 20 such facilities that have been installed throughout the United States. Also take a look at the One Wilshire building where 260 ISP's connections converge into one building. That location is a prime location for an interception facility.

The fact is an ISP (or the equipment installed by the NSA in the ISP) can intercept and MITM attack an SSL connection and they can do it quite easily actually.

• Your web browser or operating system has over 500 trusted certificates installed in it. This means that you implicitly trust any website whose certificate has been signed by this certificate.
• The NSA via secret FISA court order can force any Certificate Authority operating in the United States to give them their root certificate. The court order includes a special non disclosure clause which forces the CA to keep their mouth shut under penalty of jail time if they speak out about it. They may not even need to do this however, they only need to convince the browser vendors to accept one NSA owned certificate as trusted in the browser.
• As your traffic passes through the ISP they swap out the website's true public key with the NSA's own public key signed by the compromised certificate authority thus performing the MITM attack.
• Your web browser accepts this false certificate as trusted and you communicate the symmetric encryption key for the exchange back to the NSA/ISP who keep a copy of it and also pass the same key onto the website.
• Your session with the website is decrypted in real-time with the compromised symmetric key.
• The decrypted data is sent via fibre optic line to the NSA's headquarters and data center in the basement of Fort Meade. This scans the data for hundreds or thousands of keywords that may indicate various types of threats. Any keywords are red-flagged for an analyst to view and prioritize further action if any. The final data is sent to one of the NSA's data storage facilities in the US. The new storage facility is the Utah datacenter which is likely online already as it was scheduled to be online at the end of last month.

Here's a diagram from nsawatch.org:

A lot of the answers already provided are overlooking the interception capability of the ISP or NSA. Take a look at Room 641A⁽¹⁾ in the AT&T datacenter. There are an estimated 10 to 20 such facilities that have been installed throughout the United States. Also take a look at the One Wilshire⁽²⁾ building where 260 ISP's connections converge into one building. That location is a prime location for an interception facility.

The fact is an ISP (or the equipment installed by the NSA in the ISP) can intercept and MITM attack an SSL connection and they can do it quite easily actually.

• Your web browser or operating system has over 500 trusted certificates installed in it. This means that you implicitly trust any website whose certificate has been signed by this certificate.
• The NSA via secret FISA court order can force any Certificate Authority operating in the United States to give them their root certificate. The court order includes a special non disclosure clause which forces the CA to keep their mouth shut under penalty of jail time if they speak out about it. They may not even need to do this however, they only need to convince the browser vendors to accept one NSA owned certificate as trusted in the browser.
• As your traffic passes through the ISP they swap out the website's true public key with the NSA's own public key signed by the compromised certificate authority thus performing the MITM attack.
• Your web browser accepts this false certificate as trusted and you communicate the symmetric encryption key for the exchange back to the NSA/ISP who keep a copy of it and also pass the same key onto the website.
• Your session with the website is decrypted in real-time with the compromised symmetric key.
• The decrypted data is sent via fibre optic line to the NSA's headquarters and data center⁽³⁾ in the basement of Fort Meade. This scans the data for hundreds or thousands of keywords that may indicate various types of threats. Any keywords are red-flagged for an analyst to view and prioritize further action if any. The final data is sent to one of the NSA's data storage facilities in the US. The new storage facility is the Utah datacenter⁽⁴⁾ which is likely online already as it was scheduled to be online at the end of last month.

Here's a diagram from nsawatch.org:

Here are the reference links due to 10 reputation limit for more than 1 link per post:

(1): https://en.wikipedia.org/wiki/Room_641A (2): http://royal.pingdom.com/2008/03/07/the-%E2%80%9Ctop-secret%E2%80%9D-room-where-260-internet-service-providers-connect/ (3): http://www.nsawatch.org/eaves101.html (4): https://en.wikipedia.org/wiki/Utah_Data_Center 

A lot of the answers already provided are overlooking the interception capability of the ISP or NSA. Take a look at Room 641A in the AT&T datacenter. There are an estimated 10 to 20 such facilities that have been installed throughout the United States. Also take a look at the One Wilshire building where 260 ISP's connections converge into one building. That location is a prime location for an interception facility.

The fact is an ISP (or the equipment installed by the NSA in the ISP) can intercept and MITM attack an SSL connection and they can do it quite easily actually.

• Your web browser or operating system has over 500 trusted certificates installed in it. This means that you implicitly trust any website whose certificate has been signed by this certificate.
• The NSA via secret FISA court order can force any Certificate Authority operating in the United States to give them their root certificate. The court order includes a special non disclosure clause which forces the CA to keep their mouth shut under penalty of jail time if they speak out about it. They may not even need to do this however, they only need to convince the browser vendors to accept one NSA owned certificate as trusted in the browser.
• As your traffic passes through the ISP they swap out the website's true public key with the NSA's own public key signed by the compromised certificate authority thus performing the MITM attack.
• Your web browser accepts this false certificate as trusted and you communicate the symmetric encryption key for the exchange back to the NSA/ISP who keep a copy of it and also pass the same key onto the website.
• Your session with the website is decrypted in real-time with the compromised symmetric key.
• The decrypted data is sent via fibre optic line to the NSA's headquarters and data center in the basement of Fort Meade. This scans the data for hundreds or thousands of keywords that may indicate various types of threats. Any keywords are red-flagged for an analyst to view and prioritize further action if any. The final data is sent to one of the NSA's data storage facilities in the US. The new storage facility is the Utah datacenter which is likely online already as it was scheduled to be online at the end of last month.

Here's a diagram from nsawatch.org: