Testifying before the Senate Judiciary Committee, Comey also parried questions related to the current debate over the government's use of surveillance programs and metadata to prevent terrorism.
"Where do we draw the line at going too far?" asked Sen. Mazie Hirono, D-Hawaii.
Comey said he did not know details of the current programs to be able to answer her question. But at one point he offered an endorsement of greater transparency.
"I think the transparency is a key value, especially when it helps the American people understand what the government is doing to try to keep them safe," Comey said. "And I think if they understood more, they would feel better about it. But at the same time, I'm not in a position to judge what is on the other side. I wouldn't want to let transparency be the only value."
Discussing Comey's role in the interrogation practices of the Bush administration, Sen. Patrick Leahy, D-Vt., chairman of the panel, expressed concerns over the memos Comey had signed while at Justice approving certain tactics, which included waterboarding.
Comey said that he believed the 1994 federal anti-torture statute was vague in its application to interrogation techniques, and while he tried to halt use of the tactic, he was unsuccessful.
But Sen. John Cornyn, R-Texas, said that he believed that the Obama administration's refusal to use enhanced interrogation techniques is harmful to national security.
"We don't have a lot of information that we might have otherwise been able to get from an intelligence gathering perspective, and that strikes me as problematic," he said.
If confirmed by the Senate, Comey, a former federal prosecutor, would succeed FBI Director Robert Mueller. His background appears to have secured bipartisan support on Capital Hill, but civil liberties groups and some Democrats have voiced concerns about his record of signing off on tactics employed by the Bush administration to go after and prosecute suspected terrorists.
Comey, however, stiff-armed some of those methods in a now-famous 2004 nighttime episode at the bedside of Ashcroft, when the attorney general was hospitalized and had temporarily transferred his authority to Comey.
Top Bush administration officials went to hospital to persuade the ailing Ashcroft, despite his condition, to approve warrantless surveillance. Comey arrived at the hospital before the Bush officials and as acting attorney general blocked their attempts.